diff --git a/Sources/RubyGateway/CRubyMacros.swift b/Sources/RubyGateway/CRubyMacros.swift
index 1a6325d..c102c3c 100644
--- a/Sources/RubyGateway/CRubyMacros.swift
+++ b/Sources/RubyGateway/CRubyMacros.swift
@@ -25,13 +25,13 @@ internal import RubyGatewayHelpers
 
 // From platform to NUM -- BIGNUM or FIXNUM depending on size.
 
-func RB_LONG2NUM(_ x: Int) -> VALUE      { return rb_long2num_inline(x) }
-func RB_ULONG2NUM(_ x: UInt) -> VALUE    { return rb_ulong2num_inline(x) }
+func RB_LONG2NUM(_ x: Int) -> VALUE      { rb_long2num_inline(x) }
+func RB_ULONG2NUM(_ x: UInt) -> VALUE    { rb_ulong2num_inline(x) }
 
 // MARK: - Floating point conversions
 
 // From platform to NUM -- FLONUM or CLASS(FLOAT) depending
-func DBL2NUM(_ dbl: Double) -> VALUE { return rb_float_new(dbl) }
+func DBL2NUM(_ dbl: Double) -> VALUE { rb_float_new(dbl) }
 
 // MARK: - Useful VALUE constants and macros
 
diff --git a/Sources/RubyGateway/RbBlockCall.swift b/Sources/RubyGateway/RbBlockCall.swift
index b2a742b..e8aa67e 100644
--- a/Sources/RubyGateway/RbBlockCall.swift
+++ b/Sources/RubyGateway/RbBlockCall.swift
@@ -107,7 +107,7 @@ private class RbBlockContext {
         // A EXC_BAD_ACCESS here usually means the blockRetention has been
         // set wrongly - at any rate, the `RbProcContext` has been deallocated
         // while Ruby was still using it.
-        return Unmanaged<RbBlockContext>.fromOpaque(raw).takeUnretainedValue()
+        Unmanaged<RbBlockContext>.fromOpaque(raw).takeUnretainedValue()
     }
 }
 
diff --git a/Sources/RubyGateway/RbClass.swift b/Sources/RubyGateway/RbClass.swift
index b34e3a7..aac0517 100644
--- a/Sources/RubyGateway/RbClass.swift
+++ b/Sources/RubyGateway/RbClass.swift
@@ -20,7 +20,7 @@ private protocol RbBoundClassProtocol {
 }
 
 private struct RbBoundClass<T: AnyObject> : RbBoundClassProtocol {
-    var initializer: () -> T
+    let initializer: () -> T
 
     func createInstance() -> UnsafeMutableRawPointer {
         let instance = initializer()
diff --git a/Sources/RubyGateway/RbComplex.swift b/Sources/RubyGateway/RbComplex.swift
index 928d21d..64309f7 100644
--- a/Sources/RubyGateway/RbComplex.swift
+++ b/Sources/RubyGateway/RbComplex.swift
@@ -52,7 +52,7 @@ public struct RbComplex: RbObjectConvertible {
     /// ```swift
     /// let compl = RbComplex("1+2.3i")
     /// ```
-    public init?(_ value: RbObjectConvertible) {
+    public init?(_ value: any RbObjectConvertible) {
         self.init(value.rubyObject)
     }
 
diff --git a/Sources/RubyGateway/RbConversions.swift b/Sources/RubyGateway/RbConversions.swift
index 1636355..f02af5b 100644
--- a/Sources/RubyGateway/RbConversions.swift
+++ b/Sources/RubyGateway/RbConversions.swift
@@ -34,7 +34,7 @@ extension RbObject {
     ///
     /// RubyGateway conforms most of the Swift standard library types
     /// to `RbObjectConvertible`.
-    public convenience init(_ value: RbObjectConvertible) {
+    public convenience init(_ value: any RbObjectConvertible) {
         self.init(value.rubyObject)
     }
 }
@@ -44,7 +44,7 @@ extension RbObject: RbObjectConvertible {
     /// Returns `self`, the `RbObject`.
     ///
     /// :nodoc:
-    public var rubyObject: RbObject { return self }
+    public var rubyObject: RbObject { self }
     // Quick sanity check here: RbObject is a ref type so this `return self` is OK,
     // it returns a second ref-counted ptr to the single `RbObj` which has a single
     // `Rbb_val`.  There is no aliasing of `Rbb_val` ownership.
@@ -169,7 +169,7 @@ extension Bool: RbObjectConvertible {
 
     /// A Ruby object for the boolean value.
     public var rubyObject: RbObject {
-        return RbObject(rubyValue: self ? Qtrue : Qfalse)
+        RbObject(rubyValue: self ? Qtrue : Qfalse)
     }
 }
 
@@ -352,7 +352,7 @@ extension Array: RbObjectConvertible where Element: RbObjectConvertible {
 extension ArraySlice: RbObjectConvertible where Element: RbObjectConvertible {
     /// No sense in converting :nodoc:
     public init?(_ value: RbObject) {
-        return nil
+        nil
     }
 
     /// Create a Ruby array object for this `ArraySlice`.  All the sliceness
@@ -489,8 +489,8 @@ extension Optional: RbObjectConvertible where Wrapped == RbObjectConvertible {
 
     public var rubyObject: RbObject {
         switch self {
-        case .some(let w): return w.rubyObject
-        case .none: return .nilObject
+        case .some(let w): w.rubyObject
+        case .none: .nilObject
         }
     }
 }
@@ -517,7 +517,7 @@ private func decodeRange<T>(_ object: RbObject, halfOpen: Bool) -> (T, T)? where
 
 /// Helper to create a Ruby Range from Swift types.
 private func makeRange<T>(lower: T, upper: T, halfOpen: Bool) -> RbObject where T: RbObjectConvertible {
-    return RbObject(ofClass: "Range", args: [lower, upper, halfOpen]) ?? .nilObject
+    RbObject(ofClass: "Range", args: [lower, upper, halfOpen]) ?? .nilObject
 }
 
 // One day Swift will catch up with C++ and let me write this as a single generic...
@@ -538,7 +538,7 @@ extension Range: RbObjectConvertible where Bound: RbObjectConvertible {
 
     /// A Ruby object for the range.
     public var rubyObject: RbObject {
-        return makeRange(lower: lowerBound, upper: upperBound, halfOpen: true)
+        makeRange(lower: lowerBound, upper: upperBound, halfOpen: true)
     }
 }
 
@@ -560,7 +560,7 @@ extension ClosedRange: RbObjectConvertible where Bound: RbObjectConvertible {
 
     /// A Ruby object for the range.
     public var rubyObject: RbObject {
-        return makeRange(lower: lowerBound, upper: upperBound, halfOpen: false)
+        makeRange(lower: lowerBound, upper: upperBound, halfOpen: false)
     }
 }
 
diff --git a/Sources/RubyGateway/RbError.swift b/Sources/RubyGateway/RbError.swift
index c63c25d..230e90c 100644
--- a/Sources/RubyGateway/RbError.swift
+++ b/Sources/RubyGateway/RbError.swift
@@ -12,7 +12,6 @@ internal import RubyGatewayHelpers
 /// generates `RbError.rubyJump(_:)`, and the other cases correspond
 /// to error conditions encountered by the Swift software.
 public enum RbError: Error {
-
     // MARK: - Cases
 
     /// The Ruby VM could not be set up.
@@ -124,19 +123,19 @@ extension RbError: CustomStringConvertible {
     public var description: String {
         switch self {
         case let .setup(msg):
-            return "Can't set up Ruby: \(msg)"
+            "Can't set up Ruby: \(msg)"
         case let .badType(msg):
-            return "Object has bad type: \(msg)"
+            "Object has bad type: \(msg)"
         case let .badParameter(msg):
-            return "Parameter has bad value: \(msg)"
+            "Parameter has bad value: \(msg)"
         case let .badIdentifier(type, id):
-            return "Bad Ruby identifier: '\(id)' does not look like \(type) name."
+            "Bad Ruby identifier: '\(id)' does not look like \(type) name."
         case let .duplicateKwArg(key):
-            return "Duplicate keyword arg \(key) on call()."
+            "Duplicate keyword arg \(key) on call()."
         case let .rubyException(exn):
-            return "Ruby exception: \(exn)"
+            "Ruby exception: \(exn)"
         case let .rubyJump(tag):
-            return "Ruby jump flow control: \(tag)"
+            "Ruby jump flow control: \(tag)"
         }
     }
 }
@@ -162,7 +161,7 @@ public struct RbBreak: Error {
     ///
     /// - parameter object: the value to give as the result of the iteration.
     ///                     Default `nil` equivalent to raw `break` in Ruby.
-    public init(with object: RbObjectConvertible? = nil) {
+    public init(with object: (any RbObjectConvertible)? = nil) {
         self.object = object?.rubyObject
     }
 }
diff --git a/Sources/RubyGateway/RbFailableAccess.swift b/Sources/RubyGateway/RbFailableAccess.swift
index b5f8566..5faeed9 100644
--- a/Sources/RubyGateway/RbFailableAccess.swift
+++ b/Sources/RubyGateway/RbFailableAccess.swift
@@ -39,7 +39,7 @@ extension RbObjectAccess {
     /// Get a version of this API that returns `nil` instead of throwing errors.
     /// See `RbFailableAccess`.
     public var failable: RbFailableAccess {
-        return RbFailableAccess(access: self)
+        RbFailableAccess(access: self)
     }
 }
 
@@ -56,9 +56,9 @@ extension RbFailableAccess {
     /// - parameter kwArgs: The keyword arguments to the method, none by default.
     /// - returns: An `RbObject` for the result of the method, or `nil` if an error occurred.
     public func call(_ method: String,
-                     args: [RbObjectConvertible?] = [],
-                     kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:]) -> RbObject? {
-        return try? access.call(method, args: args, kwArgs: kwArgs)
+                     args: [(any RbObjectConvertible)?] = [],
+                     kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:]) -> RbObject? {
+        try? access.call(method, args: args, kwArgs: kwArgs)
     }
 
     /// Call a method of a Ruby object passing Swift code as a block.
@@ -74,11 +74,11 @@ extension RbFailableAccess {
     /// - parameter blockCall: Swift code to pass as a block to the method.
     /// - returns: An `RbObject` for the result of the method, or `nil` if an error occurred.
     public func call(_ method: String,
-                     args: [RbObjectConvertible?] = [],
-                     kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:],
+                     args: [(any RbObjectConvertible)?] = [],
+                     kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:],
                      blockRetention: RbBlockRetention = .none,
                      blockCall: @escaping RbBlockCallback) -> RbObject? {
-        return try? access.call(method, args: args, kwArgs: kwArgs, blockRetention: blockRetention, blockCall: blockCall)
+        try? access.call(method, args: args, kwArgs: kwArgs, blockRetention: blockRetention, blockCall: blockCall)
     }
 
     /// Call a method of a Ruby object passing a Ruby Proc as a block.
@@ -92,10 +92,10 @@ extension RbFailableAccess {
     /// - parameter block: A Ruby proc to pass as a block to the method.
     /// - returns: An `RbObject` for the result of the method, or `nil` if an error occurred.
     public func call(_ method: String,
-                     args: [RbObjectConvertible?] = [],
-                     kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:],
-                     block: RbObjectConvertible) -> RbObject? {
-        return try? access.call(method, args: args, kwArgs: kwArgs, block: block)
+                     args: [(any RbObjectConvertible)?] = [],
+                     kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:],
+                     block: any RbObjectConvertible) -> RbObject? {
+        try? access.call(method, args: args, kwArgs: kwArgs, block: block)
     }
 
     /// Call a method of a Ruby object using a symbol.
@@ -108,10 +108,10 @@ extension RbFailableAccess {
     /// - parameter kwArgs: The keyword arguments to the method, none by default.
     /// - returns: An `RbObject` for the result of the method, or `nil` if an error occurred.
     @discardableResult
-    public func call(symbol: RbObjectConvertible,
-                     args: [RbObjectConvertible?] = [],
-                     kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:]) -> RbObject? {
-        return try? access.call(symbol: symbol, args: args, kwArgs: kwArgs)
+    public func call(symbol: any RbObjectConvertible,
+                     args: [(any RbObjectConvertible)?] = [],
+                     kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:]) -> RbObject? {
+        try? access.call(symbol: symbol, args: args, kwArgs: kwArgs)
     }
 
     /// Call a method of a Ruby object using a symbol passing Swift code as a block.
@@ -127,12 +127,12 @@ extension RbFailableAccess {
     /// - parameter blockCall: Swift code to pass as a block to the method.
     /// - returns: An `RbObject` for the result of the method, or `nil` if an error occurred.
     @discardableResult
-    public func call(symbol: RbObjectConvertible,
-                     args: [RbObjectConvertible?] = [],
-                     kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:],
+    public func call(symbol: any RbObjectConvertible,
+                     args: [(any RbObjectConvertible)?] = [],
+                     kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:],
                      blockRetention: RbBlockRetention = .none,
                      blockCall: @escaping RbBlockCallback) -> RbObject? {
-        return try? access.call(symbol: symbol, args: args, kwArgs: kwArgs, blockRetention: blockRetention, blockCall: blockCall)
+        try? access.call(symbol: symbol, args: args, kwArgs: kwArgs, blockRetention: blockRetention, blockCall: blockCall)
     }
 
     /// Call a method of a Ruby object using a symbol passing a Ruby Proc as a block.
@@ -146,11 +146,11 @@ extension RbFailableAccess {
     /// - parameter block: A Ruby proc to pass as a block to the method.
     /// - returns: An `RbObject` for the result of the method, or `nil` if an error occurred.
     @discardableResult
-    public func call(symbol: RbObjectConvertible,
-                     args: [RbObjectConvertible?] = [],
-                     kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:],
-                     block: RbObjectConvertible) -> RbObject? {
-        return try? access.call(symbol: symbol, args: args, kwArgs: kwArgs, block: block)
+    public func call(symbol: any RbObjectConvertible,
+                     args: [(any RbObjectConvertible)?] = [],
+                     kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:],
+                     block: any RbObjectConvertible) -> RbObject? {
+        try? access.call(symbol: symbol, args: args, kwArgs: kwArgs, block: block)
     }
 }
 
@@ -165,7 +165,7 @@ extension RbFailableAccess {
     /// - parameter name: The attribute to access.
     /// - returns: The value of the attribute, or `nil` if an error occurred.
     public func getAttribute(_ name: String) -> RbObject? {
-        return try? access.getAttribute(name)
+        try? access.getAttribute(name)
     }
 
     /// Set an attribute of a Ruby object.
@@ -176,8 +176,8 @@ extension RbFailableAccess {
     /// - parameter name: The attribute to set.
     /// - parameter newValue: The new value for the attribute.
     /// - returns: The value set to the attribute, or `nil` if an error occurred.
-    public func setAttribute(_ name: String, newValue: RbObjectConvertible?) -> RbObject? {
-        return try? access.setAttribute(name, newValue: newValue)
+    public func setAttribute(_ name: String, newValue: (any RbObjectConvertible)?) -> RbObject? {
+        try? access.setAttribute(name, newValue: newValue)
     }
 }
 
@@ -192,7 +192,7 @@ extension RbFailableAccess {
     /// - parameter name: The name of the constant to look up.
     /// - returns: An `RbObject` for the constant or `nil` if an error occurred.
     public func getConstant(_ name: String) -> RbObject? {
-        return try? access.getConstant(name)
+        try? access.getConstant(name)
     }
 
     /// Get an `RbObject` that represents a Ruby class.
@@ -203,7 +203,7 @@ extension RbFailableAccess {
     /// - parameter name: The name of the class to look up.
     /// - returns: An `RbObject` for the class or `nil` if an error occurred.
     public func getClass(_ name: String) -> RbObject? {
-        return try? access.getClass(name)
+        try? access.getClass(name)
     }
 
     /// Bind an object to a constant name.
@@ -215,8 +215,8 @@ extension RbFailableAccess {
     /// - parameter newValue: The value for the constant.
     /// - returns: The value set for the constant or `nil` if an error occurred.
     @discardableResult
-    public func setConstant(_ name: String, newValue: RbObjectConvertible?) -> RbObject? {
-        return try? access.setConstant(name, newValue: newValue)
+    public func setConstant(_ name: String, newValue: (any RbObjectConvertible)?) -> RbObject? {
+        try? access.setConstant(name, newValue: newValue)
     }
 }
 
@@ -231,7 +231,7 @@ extension RbFailableAccess {
     /// - parameter name: Name of the IVar.  Must begin with a single `@`.
     /// - returns: Value of the IVar, or `nil` if an error occurred.
     public func getInstanceVar(_ name: String) -> RbObject? {
-        return try? access.getInstanceVar(name)
+        try? access.getInstanceVar(name)
     }
 
     /// Set a Ruby instance variable.
@@ -243,8 +243,8 @@ extension RbFailableAccess {
     /// - parameter newValue: The new value for the IVar.
     /// - returns: The value that was set, or nil if an error occurred.
     @discardableResult
-    public func setInstanceVar(_ name: String, newValue: RbObjectConvertible?) -> RbObject? {
-        return try? access.setInstanceVar(name, newValue: newValue)
+    public func setInstanceVar(_ name: String, newValue: (any RbObjectConvertible)?) -> RbObject? {
+        try? access.setInstanceVar(name, newValue: newValue)
     }
 }
 
@@ -261,7 +261,7 @@ extension RbFailableAccess {
     /// - parameter name: Name of the CVar.  Must begin with `@@`.
     /// - returns: Value of the CVar, or `nil` if an error occurred.
     public func getClassVar(_ name: String) -> RbObject? {
-        return try? access.getClassVar(name)
+        try? access.getClassVar(name)
     }
 
     /// Set or create a Ruby class variable.
@@ -275,8 +275,8 @@ extension RbFailableAccess {
     /// - parameter newValue: The new value for the CVar.
     /// - returns: The value that was set, or `nil` if an error occurred.
     @discardableResult
-    public func setClassVar(_ name: String, newValue: RbObjectConvertible?) -> RbObject? {
-        return try? access.setClassVar(name, newValue: newValue)
+    public func setClassVar(_ name: String, newValue: (any RbObjectConvertible)?) -> RbObject? {
+        try? access.setClassVar(name, newValue: newValue)
     }
 }
 
@@ -291,7 +291,7 @@ extension RbFailableAccess {
     /// - parameter name: Name of the global variable.  Must begin with `$`.
     /// - returns: Value of the variable, or `nil` if an error occurred.
     public func getGlobalVar(_ name: String) -> RbObject? {
-        return try? access.getGlobalVar(name)
+        try? access.getGlobalVar(name)
     }
 
     /// Set a Ruby global variable.
@@ -303,8 +303,8 @@ extension RbFailableAccess {
     /// - parameter newValue: The new value for the variable.
     /// - returns: The value that was set, or `nil` if an error occurred.
     @discardableResult
-    public func setGlobalVar(_ name: String, newValue: RbObjectConvertible?) -> RbObject? {
-        return try? access.setGlobalVar(name, newValue: newValue)
+    public func setGlobalVar(_ name: String, newValue: (any RbObjectConvertible)?) -> RbObject? {
+        try? access.setGlobalVar(name, newValue: newValue)
     }
 }
 
@@ -320,6 +320,6 @@ extension RbFailableAccess {
     /// - returns: Retrieved object, or `nil` if an error occurred.
     @discardableResult
     public func get(_ name: String) -> RbObject? {
-        return try? access.get(name)
+        try? access.get(name)
     }
 }
diff --git a/Sources/RubyGateway/RbGateway.swift b/Sources/RubyGateway/RbGateway.swift
index f362a40..c484d36 100644
--- a/Sources/RubyGateway/RbGateway.swift
+++ b/Sources/RubyGateway/RbGateway.swift
@@ -159,7 +159,7 @@ public final class RbGateway: RbObjectAccess, @unchecked Sendable {
     /// - throws: `RbError.badIdentifier(type:id:)` if `name` looks wrong.
     ///           `RbError.rubyException(_:)` if Ruby has a problem.
     @discardableResult
-    public override func setInstanceVar(_ name: String, newValue: RbObjectConvertible?) throws -> RbObject {
+    public override func setInstanceVar(_ name: String, newValue: (any RbObjectConvertible)?) throws -> RbObject {
         try setup()
         try name.checkRubyInstanceVarName()
 
@@ -309,7 +309,7 @@ extension RbGateway {
     public func require(filename: String) throws -> Bool {
         // Have to use eval so that gems work - rubygems/kernel_require.rb replaces
         // `Kernel#require` so it can do the gem thing, so `rb_require` is no good.
-        return try eval(ruby: "require '\(filename)'").isTruthy
+        try eval(ruby: "require '\(filename)'").isTruthy
     }
 
     /// See Ruby `Kernel#load`. Load a file, reloads if already loaded.
diff --git a/Sources/RubyGateway/RbGlobalVar.swift b/Sources/RubyGateway/RbGlobalVar.swift
index 6364900..c5e091d 100644
--- a/Sources/RubyGateway/RbGlobalVar.swift
+++ b/Sources/RubyGateway/RbGlobalVar.swift
@@ -14,7 +14,7 @@ internal import RubyGatewayHelpers
 // MARK: Callbacks from C code (rbg_value.m)
 
 private func rbobject_gvar_get_callback(id: ID) -> VALUE {
-    return RbGlobalVar.get(id: id)
+    RbGlobalVar.get(id: id)
 }
 
 private func rbobject_gvar_set_callback(id: ID,
diff --git a/Sources/RubyGateway/RbMethod.swift b/Sources/RubyGateway/RbMethod.swift
index 44e5c0b..f9505f6 100644
--- a/Sources/RubyGateway/RbMethod.swift
+++ b/Sources/RubyGateway/RbMethod.swift
@@ -107,8 +107,8 @@ private struct RbMethodId: Hashable {
     let mid: Rbg_method_id
 
     public static func == (lhs: RbMethodId, rhs: RbMethodId) -> Bool {
-        return (lhs.mid.method == rhs.mid.method) &&
-               (lhs.mid.target == rhs.mid.target)
+        (lhs.mid.method == rhs.mid.method) &&
+            (lhs.mid.target == rhs.mid.target)
     }
 
     public func hash(into hasher: inout Hasher) {
@@ -123,7 +123,7 @@ private struct RbMethodExec {
     let argsSpec: RbMethodArgsSpec
 
     /// The Swift implementation of the method.
-    var callback: RbMethodCallback
+    let callback: RbMethodCallback
 
     /// Validate the given args against the spec and if good,
     /// invoke the user function.
@@ -205,7 +205,7 @@ public struct RbMethod {
 
     /// Has the method been passed a block?
     public var isBlockGiven: Bool {
-        return rb_block_given_p() != 0
+        rb_block_given_p() != 0
     }
 
     /// Raise an exception if the method has not been passed a block.
@@ -227,8 +227,8 @@ public struct RbMethod {
     ///     You should not attempt to handle `rubyJump` errors: rethrow them
     ///     back to Ruby as soon as possible.
     @discardableResult
-    public func yieldBlock(args: [RbObjectConvertible?] = [],
-                           kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:]) throws -> RbObject {
+    public func yieldBlock(args: [(any RbObjectConvertible)?] = [],
+                           kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:]) throws -> RbObject {
         let rubyArgs = try RbObjectAccess.flattenArgs(args: args, kwArgs: kwArgs)
         return RbObject(rubyValue: try rubyArgs.withRubyValues { argValues in
             try RbVM.doProtect { tag in
@@ -263,8 +263,8 @@ public struct RbMethod {
     /// - Returns: The value returned by the superclass method.
     /// - Throws: `RbError.rubyException(_:)` if there is a Ruby exception.
     ///           `RbError.duplicateKwArg(_:)` if there are duplicate keywords in `kwArgs`.
-    public func callSuper(args: [RbObjectConvertible?] = [],
-                          kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:]) throws -> RbObject {
+    public func callSuper(args: [(any RbObjectConvertible)?] = [],
+                          kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:]) throws -> RbObject {
         let rubyArgs = try RbObjectAccess.flattenArgs(args: args, kwArgs: kwArgs)
         return RbObject(rubyValue: try rubyArgs.withRubyValues { rubyValues in
             try RbVM.doProtect { tag in
@@ -324,7 +324,7 @@ public struct RbMethodArgsSpec {
     public let optionalValues: [() -> RbObject]
     /// The number of optional positional arguments.
     public var optionalCount: Int {
-        return optionalValues.count
+        optionalValues.count
     }
     /// Does the method support variable-length splatted arguments?
     public let supportsSplat: Bool
@@ -332,7 +332,7 @@ public struct RbMethodArgsSpec {
     public let trailingMandatoryCount: Int
     /// The number of all mandatory positional arguments.
     public var totalMandatoryCount: Int {
-        return leadingMandatoryCount + trailingMandatoryCount
+        leadingMandatoryCount + trailingMandatoryCount
     }
     /// Names of mandatory keyword arguments.
     public let mandatoryKeywords: Set<String>
@@ -340,7 +340,7 @@ public struct RbMethodArgsSpec {
     public let optionalKeywordValues: [String : () -> RbObject]
     /// Does the method support keyword arguments?
     public var supportsKeywords: Bool {
-        return mandatoryKeywords.count > 0 || optionalKeywordValues.count > 0
+        mandatoryKeywords.count > 0 || optionalKeywordValues.count > 0
     }
     /// Does the method require a block?
     public let requiresBlock: Bool
@@ -373,11 +373,11 @@ public struct RbMethodArgsSpec {
     ///   - requiresBlock: Whether the method requires a block, `false` by default.  If this is
     ///     `true` then the method may or may not be called with a block.
     public init(leadingMandatoryCount: Int = 0,
-                optionalValues: [RbObjectConvertible?] = [],
+                optionalValues: [(any RbObjectConvertible)?] = [],
                 supportsSplat: Bool = false,
                 trailingMandatoryCount: Int = 0,
                 mandatoryKeywords: Set<String> = [],
-                optionalKeywordValues: [String: RbObjectConvertible?] = [:],
+                optionalKeywordValues: [String: (any RbObjectConvertible)?] = [:],
                 requiresBlock: Bool = false) {
         self.leadingMandatoryCount = leadingMandatoryCount
         self.optionalValues = optionalValues.map { val in { val.rubyObject } }
@@ -399,7 +399,7 @@ public struct RbMethodArgsSpec {
     /// - parameter count: the number of arguments not including any block that the
     ///                    method must be passed.
     public static func basic(_ count: Int) -> RbMethodArgsSpec {
-        return RbMethodArgsSpec(leadingMandatoryCount: count)
+        RbMethodArgsSpec(leadingMandatoryCount: count)
     }
 
     /// Decode the arguments passed to a function and make them available.
diff --git a/Sources/RubyGateway/RbNumericConversions.swift b/Sources/RubyGateway/RbNumericConversions.swift
index 1c948e4..73cf64b 100644
--- a/Sources/RubyGateway/RbNumericConversions.swift
+++ b/Sources/RubyGateway/RbNumericConversions.swift
@@ -30,7 +30,7 @@ extension UInt64: RbObjectConvertible {
 
     /// A Ruby object for the number.
     public var rubyObject: RbObject {
-        return UInt(self).rubyObject
+        UInt(self).rubyObject
     }
 }
 
@@ -54,7 +54,7 @@ extension UInt32: RbObjectConvertible {
 
     /// A Ruby object for the number.
     public var rubyObject: RbObject {
-        return UInt(self).rubyObject
+        UInt(self).rubyObject
     }
 }
 
@@ -78,7 +78,7 @@ extension UInt16: RbObjectConvertible {
 
     /// A Ruby object for the number.
     public var rubyObject: RbObject {
-        return UInt(self).rubyObject
+        UInt(self).rubyObject
     }
 }
 
@@ -102,7 +102,7 @@ extension UInt8: RbObjectConvertible {
 
     /// A Ruby object for the number.
     public var rubyObject: RbObject {
-        return UInt(self).rubyObject
+        UInt(self).rubyObject
     }
 }
 
@@ -127,7 +127,7 @@ extension Int64: RbObjectConvertible {
 
     /// A Ruby object for the number.
     public var rubyObject: RbObject {
-        return Int(self).rubyObject
+        Int(self).rubyObject
     }
 }
 
@@ -150,7 +150,7 @@ extension Int32: RbObjectConvertible {
 
     /// A Ruby object for the number.
     public var rubyObject: RbObject {
-        return Int(self).rubyObject
+        Int(self).rubyObject
     }
 }
 
@@ -173,7 +173,7 @@ extension Int16: RbObjectConvertible {
 
     /// A Ruby object for the number.
     public var rubyObject: RbObject {
-        return Int(self).rubyObject
+        Int(self).rubyObject
     }
 }
 
@@ -196,7 +196,7 @@ extension Int8: RbObjectConvertible {
 
     /// A Ruby object for the number.
     public var rubyObject: RbObject {
-        return Int(self).rubyObject
+        Int(self).rubyObject
     }
 }
 
@@ -226,6 +226,6 @@ extension Float: RbObjectConvertible {
 
     /// A Ruby object for the number.
     public var rubyObject: RbObject {
-        return Double(self).rubyObject
+        Double(self).rubyObject
     }
 }
diff --git a/Sources/RubyGateway/RbObject.swift b/Sources/RubyGateway/RbObject.swift
index 202e1ce..b0bd0de 100644
--- a/Sources/RubyGateway/RbObject.swift
+++ b/Sources/RubyGateway/RbObject.swift
@@ -246,8 +246,8 @@ extension RbObject {
     /// - parameter args: positional arguments to pass to `new` call for the object.  Default none.
     /// - parameter kwArgs: keyword arguments to pass to the `new` call for the object.  Default none.
     public convenience init?(ofClass className: String,
-                             args: [RbObjectConvertible?] = [],
-                             kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:]) {
+                             args: [(any RbObjectConvertible)?] = [],
+                             kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:]) {
         guard let obj = try? Ruby.get(className).call("new", args: args, kwArgs: kwArgs) else {
             return nil
         }
@@ -268,8 +268,8 @@ extension RbObject {
     ///             using `Proc#new`.
     /// - parameter blockCall: Swift code to pass as a block to the method.
     public convenience init?(ofClass className: String,
-                             args: [RbObjectConvertible?] = [],
-                             kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:],
+                             args: [(any RbObjectConvertible)?] = [],
+                             kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:],
                              retainBlock: Bool = false,
                              blockCall: @escaping RbBlockCallback) {
         let retention: RbBlockRetention = retainBlock ? .returned : .none
@@ -326,7 +326,7 @@ extension RbObject: CustomStringConvertible,
 
     /// The text from `description`.
     public var playgroundDescription: Any {
-        return description
+        description
     }
 }
 
diff --git a/Sources/RubyGateway/RbObjectAccess.swift b/Sources/RubyGateway/RbObjectAccess.swift
index c3ed848..2094668 100644
--- a/Sources/RubyGateway/RbObjectAccess.swift
+++ b/Sources/RubyGateway/RbObjectAccess.swift
@@ -109,13 +109,13 @@ public class RbObjectAccess {
     /// - throws: `RbError.badIdentifier(type:id:)` if `name` looks wrong.
     ///           `RbError.rubyException(_:)` if Ruby has a problem.
     @discardableResult
-    public func setInstanceVar(_ name: String, newValue: RbObjectConvertible?) throws -> RbObject {
+    public func setInstanceVar(_ name: String, newValue: (any RbObjectConvertible)?) throws -> RbObject {
         try Ruby.setup()
         try name.checkRubyInstanceVarName()
         let id = try Ruby.getID(for: name)
 
         return RbObject(rubyValue: newValue.rubyObject.withRubyValue { newRubyValue in
-            return rb_ivar_set(getValue(), id, newRubyValue)
+            rb_ivar_set(getValue(), id, newRubyValue)
         })
     }
 }
@@ -189,7 +189,7 @@ extension RbObjectAccess {
     ///           `rubyException(_:)` if there is a Ruby exception.
     ///           `RbError.badType(_:)` if the current object is not a class or module.
     @discardableResult
-    public func setConstant(_ name: String, newValue: RbObjectConvertible?) throws -> RbObject {
+    public func setConstant(_ name: String, newValue: (any RbObjectConvertible)?) throws -> RbObject {
         try Ruby.setup()
         try name.checkRubyConstantPath()
 
@@ -266,8 +266,8 @@ extension RbObjectAccess {
     /// For a version that does not throw, see `failable`.
     @discardableResult
     public func call(_ methodName: String,
-                     args: [RbObjectConvertible?] = [],
-                     kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:]) throws -> RbObject {
+                     args: [(any RbObjectConvertible)?] = [],
+                     kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:]) throws -> RbObject {
         try Ruby.setup()
         let methodId = try Ruby.getID(for: methodName)
         return try doCall(id: methodId, args: args, kwArgs: kwArgs)
@@ -288,8 +288,8 @@ extension RbObjectAccess {
     /// For a version that does not throw, see `failable`.
     @discardableResult
     public func call(_ methodName: String,
-                     args: [RbObjectConvertible?] = [],
-                     kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:],
+                     args: [(any RbObjectConvertible)?] = [],
+                     kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:],
                      blockRetention: RbBlockRetention = .none,
                      blockCall: @escaping RbBlockCallback) throws -> RbObject {
         try Ruby.setup()
@@ -314,9 +314,9 @@ extension RbObjectAccess {
     /// For a version that does not throw, see `failable`.
     @discardableResult
     public func call(_ methodName: String,
-                     args: [RbObjectConvertible?] = [],
-                     kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:],
-                     block: RbObjectConvertible) throws -> RbObject {
+                     args: [(any RbObjectConvertible)?] = [],
+                     kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:],
+                     block: any RbObjectConvertible) throws -> RbObject {
         try Ruby.setup()
         let methodId = try Ruby.getID(for: methodName)
         return try doCall(id: methodId, args: args, kwArgs: kwArgs, block: block)
@@ -334,9 +334,9 @@ extension RbObjectAccess {
     ///
     /// For a version that does not throw, see `failable`.
     @discardableResult
-    public func call(symbol: RbObjectConvertible,
-                     args: [RbObjectConvertible?] = [],
-                     kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:]) throws -> RbObject {
+    public func call(symbol: any RbObjectConvertible,
+                     args: [(any RbObjectConvertible)?] = [],
+                     kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:]) throws -> RbObject {
         try Ruby.setup()
         return try symbol.rubyObject.withSymbolId { methodId in
             try doCall(id: methodId, args: args, kwArgs: kwArgs)
@@ -358,9 +358,9 @@ extension RbObjectAccess {
     ///
     /// For a version that does not throw, see `failable`.
     @discardableResult
-    public func call(symbol: RbObjectConvertible,
-                     args: [RbObjectConvertible?] = [],
-                     kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:],
+    public func call(symbol: any RbObjectConvertible,
+                     args: [(any RbObjectConvertible)?] = [],
+                     kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:],
                      blockRetention: RbBlockRetention = .none,
                      blockCall: @escaping RbBlockCallback) throws -> RbObject {
         try Ruby.setup()
@@ -383,10 +383,10 @@ extension RbObjectAccess {
     ///
     /// For a version that does not throw, see `failable`.
     @discardableResult
-    public func call(symbol: RbObjectConvertible,
-                     args: [RbObjectConvertible?] = [],
-                     kwArgs: KeyValuePairs<String, RbObjectConvertible?> = [:],
-                     block: RbObjectConvertible) throws -> RbObject {
+    public func call(symbol: any RbObjectConvertible,
+                     args: [(any RbObjectConvertible)?] = [],
+                     kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?> = [:],
+                     block: any RbObjectConvertible) throws -> RbObject {
         try Ruby.setup()
         return try symbol.rubyObject.withSymbolId { methodId in
             try doCall(id: methodId, args: args, kwArgs: kwArgs, block: block)
@@ -395,10 +395,10 @@ extension RbObjectAccess {
 
     /// Backend to method-call / message-send.
     private func doCall(id: ID, 
-                        args: [RbObjectConvertible?],
-                        kwArgs: KeyValuePairs<String, RbObjectConvertible?>,
+                        args: [(any RbObjectConvertible)?],
+                        kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?>,
                         blockRetention: RbBlockRetention = .none,
-                        block: RbObjectConvertible? = nil,
+                        block: (any RbObjectConvertible)? = nil,
                         blockCall: RbBlockCallback? = nil) throws -> RbObject {
         // Sort out unlikely block errors
         let blockObj: RbObject?
@@ -452,9 +452,8 @@ extension RbObjectAccess {
     }
 
     /// Helper to massage Swift-format args ready for the API
-    internal static func flattenArgs(args: [RbObjectConvertible?],
-                                     kwArgs: KeyValuePairs<String, RbObjectConvertible?>) throws -> [RbObject] {
-
+    internal static func flattenArgs(args: [(any RbObjectConvertible)?],
+                                     kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?>) throws -> [RbObject] {
         var argObjects = args.map { $0.rubyObject }
 
         if kwArgs.count > 0 {
@@ -464,7 +463,7 @@ extension RbObjectAccess {
     }
 
     /// Build a keyword args hash.  The keys are Symbols of the keywords.
-    private static func buildKwArgsHash(from kwArgs: KeyValuePairs<String, RbObjectConvertible?>) throws -> RbObject {
+    private static func buildKwArgsHash(from kwArgs: KeyValuePairs<String, (any RbObjectConvertible)?>) throws -> RbObject {
         let hashValue = rb_hash_new()
         try kwArgs.forEach { (key, value) in
             try RbSymbol(key).rubyObject.withRubyValue { symValue in
@@ -514,7 +513,7 @@ extension RbObjectAccess {
     ///           `RbError.rubyException(_:)` if Ruby has a problem, probably means
     ///           `attribute` doesn't exist.
     @discardableResult
-    public func setAttribute(_ name: String, newValue: RbObjectConvertible?) throws -> RbObject {
+    public func setAttribute(_ name: String, newValue: (any RbObjectConvertible)?) throws -> RbObject {
         try name.checkRubyMethodName()
         return try call("\(name)=", args: [newValue])
     }
@@ -575,7 +574,7 @@ extension RbObjectAccess {
     ///           `RbError.badType(_:)` if the object is not a class.
     ///           `RbError.rubyException(_:)` if Ruby has a problem.
     @discardableResult
-    public func setClassVar(_ name: String, newValue: RbObjectConvertible?) throws -> RbObject {
+    public func setClassVar(_ name: String, newValue: (any RbObjectConvertible)?) throws -> RbObject {
         try Ruby.setup()
         try name.checkRubyClassVarName()
         try hasClassVars()
@@ -626,7 +625,7 @@ extension RbObjectAccess {
     /// make construction of `RbFailableAccess` a bit easier.  Best practice probably
     /// to avoid calling the `RbObject` version.)
     @discardableResult
-    public func setGlobalVar(_ name: String, newValue: RbObjectConvertible?) throws -> RbObject {
+    public func setGlobalVar(_ name: String, newValue: (any RbObjectConvertible)?) throws -> RbObject {
         try Ruby.setup()
         try name.checkRubyGlobalVarName()
 
diff --git a/Sources/RubyGateway/RbObjectCollection.swift b/Sources/RubyGateway/RbObjectCollection.swift
index 951eacf..9f10dc7 100644
--- a/Sources/RubyGateway/RbObjectCollection.swift
+++ b/Sources/RubyGateway/RbObjectCollection.swift
@@ -42,7 +42,7 @@ public struct RbObjectCollection: RandomAccessCollection,
     }
 
     public var startIndex: Int {
-        return 0
+        0
     }
 
     public var endIndex: Int {
@@ -55,7 +55,7 @@ public struct RbObjectCollection: RandomAccessCollection,
 
     public subscript(index: Int) -> RbObject {
         get {
-            return rubyObject[index]
+            rubyObject[index]
         }
         set {
             rubyObject[index] = newValue
diff --git a/Sources/RubyGateway/RbOperators.swift b/Sources/RubyGateway/RbOperators.swift
index f58ff56..978af37 100644
--- a/Sources/RubyGateway/RbOperators.swift
+++ b/Sources/RubyGateway/RbOperators.swift
@@ -169,7 +169,7 @@ extension RbObject {
     ///
     /// - note: Calls Ruby `[]` and `[]=` methods.  Crashes the process (`fatalError`)
     ///         if anything goes wrong - Swift can't throw from subscripts yet.
-    public subscript(args: RbObjectConvertible...) -> RbObject {
+    public subscript(args: any RbObjectConvertible...) -> RbObject {
         get {
             do {
                 return try call("[]", args: args)
diff --git a/Sources/RubyGateway/RbProc.swift b/Sources/RubyGateway/RbProc.swift
index a9e472d..d31a082 100644
--- a/Sources/RubyGateway/RbProc.swift
+++ b/Sources/RubyGateway/RbProc.swift
@@ -24,10 +24,10 @@ internal import RubyGatewayHelpers
 /// `RbObjectAccess.call(_:args:kwArgs:blockRetention:blockCall:)` directly,
 /// no need for either `RbProc` or `RbObject`.
 public struct RbProc: RbObjectConvertible {
-    private let sourceObject: RbObjectConvertible
+    private let sourceObject: any RbObjectConvertible
 
     /// Initialize from something that can be turned into a Ruby object.
-    public init(object: RbObjectConvertible) {
+    public init(object: any RbObjectConvertible) {
         sourceObject = object
     }
 
diff --git a/Sources/RubyGateway/RbRational.swift b/Sources/RubyGateway/RbRational.swift
index 64ccb3d..df2b089 100644
--- a/Sources/RubyGateway/RbRational.swift
+++ b/Sources/RubyGateway/RbRational.swift
@@ -68,7 +68,7 @@ public struct RbRational: RbObjectConvertible {
     /// ```swift
     /// let rat = RbRational(0.3)
     /// ```
-    public init?(_ value: RbObjectConvertible) {
+    public init?(_ value: any RbObjectConvertible) {
         self.init(value.rubyObject)
     }
 
diff --git a/Sources/RubyGateway/RbSymbol.swift b/Sources/RubyGateway/RbSymbol.swift
index da67ff0..7d255bf 100644
--- a/Sources/RubyGateway/RbSymbol.swift
+++ b/Sources/RubyGateway/RbSymbol.swift
@@ -30,7 +30,7 @@ public struct RbSymbol: RbObjectConvertible, Hashable {
     /// Always fails - no use for this, just use the `RbObject`.
     /// :nodoc:
     public init?(_ value: RbObject) {
-        return nil
+        nil
     }
 
     /// A Ruby object for the symbol
@@ -48,6 +48,6 @@ public struct RbSymbol: RbObjectConvertible, Hashable {
 extension RbSymbol: CustomStringConvertible {
     /// A textual representation of the `RbSymbol`
     public var description: String {
-        return "RbSymbol(\(name))"
+        "RbSymbol(\(name))"
     }
 }
diff --git a/Sources/RubyGateway/String+RubyGateway.swift b/Sources/RubyGateway/String+RubyGateway.swift
index 337daa7..960709c 100644
--- a/Sources/RubyGateway/String+RubyGateway.swift
+++ b/Sources/RubyGateway/String+RubyGateway.swift
@@ -52,7 +52,7 @@ extension String {
 
     /// Does the string look like a Ruby global variable name?
     var isRubyGlobalVarName: Bool {
-        return starts(with: "$")
+        starts(with: "$")
     }
 
     /// Throw if the string does not look like a global variable name.
@@ -62,7 +62,7 @@ extension String {
 
     /// Does the string look like a Ruby instance variable name?
     var isRubyInstanceVarName: Bool {
-        return starts(with: "@") && !isRubyClassVarName
+        starts(with: "@") && !isRubyClassVarName
     }
 
     /// Throw if the string does not look like an instance var name.
@@ -72,7 +72,7 @@ extension String {
 
     /// Does the string look like a Ruby class variable name?
     var isRubyClassVarName: Bool {
-        return starts(with: "@@")
+        starts(with: "@@")
     }
 
     /// Throw if the string does not look like a class var name.
@@ -82,7 +82,7 @@ extension String {
 
     /// Does the string look like a Ruby method name?
     var isRubyMethodName: Bool {
-        return !isRubyConstantName && !isRubyGlobalVarName && !isRubyInstanceVarName && !isRubyClassVarName
+        !isRubyConstantName && !isRubyGlobalVarName && !isRubyInstanceVarName && !isRubyClassVarName
     }
 
     /// Throw if the string does not look like a method name.
diff --git a/Tests/RubyGatewayTests/Helpers.swift b/Tests/RubyGatewayTests/Helpers.swift
index 40c645c..4c26a12 100644
--- a/Tests/RubyGatewayTests/Helpers.swift
+++ b/Tests/RubyGatewayTests/Helpers.swift
@@ -50,11 +50,13 @@ struct Helpers {
     /// that the test runner will treat that as a separate process.)
 
     /// Ruby files etc.
-    private static let fixturesDir: String = {  URL(fileURLWithPath: #file).deletingLastPathComponent().path + "/Fixtures" }()
+    private static let fixturesDir: String = {
+        URL(fileURLWithPath: #file).deletingLastPathComponent().path + "/Fixtures"
+    }()
 
     /// Get full path to fixture with name
     static func fixturePath(_ name: String) -> String {
-        return "\(fixturesDir)/\(name)"
+        "\(fixturesDir)/\(name)"
     }
 
     /// A weird Swift type that has distinct Swift instances
@@ -67,11 +69,11 @@ struct Helpers {
         }
 
         init?(_ value: RbObject) {
-            return nil
+            nil
         }
 
         var rubyObject: RbObject {
-            return RbObject(42)
+            RbObject(42)
         }
     }
 }