Replace state change callback closure with an actual type.

Closes #2

Author: lukeredpath

Demo Project/ResponsiveTextFieldDemo/ContentView.swift

@@ -64,7 +64,7 @@ struct ContentView: View {
                     text: $email,
                     firstResponderDemand: $emailResponderDemand.animation(),
                     configuration: .email,
-                    onFirstResponderStateChanged: { isFirstResponder in
+                    onFirstResponderStateChanged: .init { isFirstResponder in
                         withAnimation {
                             isEmailFirstResponder = isFirstResponder
                         }
@@ -90,7 +90,7 @@ struct ContentView: View {
                         isSecure: hidePassword,
                         firstResponderDemand: $passwordResponderDemand.animation(),
                         configuration: .combine(.password, .lastOfChain),
-                        onFirstResponderStateChanged: { isFirstResponder in
+                        onFirstResponderStateChanged: .init { isFirstResponder in
                             withAnimation {
                                 isPasswordFirstResponder = isFirstResponder
                             }

Sources/ResponsiveTextField/ResponsiveTextField.swift

@@ -10,9 +10,6 @@ import SwiftUI
 /// A SwiftUI wrapper around UITextField that gives precise control over the responder state.
 ///
 public struct ResponsiveTextField {
-    /// Communicates the text field's first responder state using a boolean value (is first responder).
-    public typealias FirstResponderStateChangeHandler = (Bool) -> Void
-
     /// The text field placeholder string
     let placeholder: String
 
@@ -145,6 +142,23 @@ public struct ResponsiveTextField {
 
 // MARK: - Managing the first responder state
 
+public struct FirstResponderStateChangeHandler {
+    /// A closure that will be called when the first responder state changes.
+    ///
+    /// - Parameters:
+    ///     - Bool: A boolean indicating if the text field is now the first responder or not.
+    ///
+    public var handleStateChange: (Bool) -> Void
+
+    public init(handleStateChange: @escaping (Bool) -> Void) {
+        self.handleStateChange = handleStateChange
+    }
+
+    func callAsFunction(_ isFirstResponder: Bool) {
+        handleStateChange(isFirstResponder)
+    }
+}
+
 /// Represents a request to change the text field's first responder state.
 ///
 public enum FirstResponderDemand: Equatable {