Functional view modifier

_ViewModifier.swift

import SwiftUI

struct _ViewModifier<Input: View, Output: View>: ViewModifier {
    typealias Body = Output
    typealias Content = _ViewModifier_Content<_ViewModifier<Input, Output>>
    
    var modification: (Content) -> Output
    func body(content: Content) -> Output {
        modification(content)
    }
    
}

extension View {
    func modifier<T: View>(_ viewModifier: _ViewModifier<Self, T>)
    -> ModifiedContent<Self, _ViewModifier<Self, T>> {
        _modifier(viewModifier)
    }
    
    private func _modifier<T: ViewModifier>(_ viewModifier: T)
    -> ModifiedContent<Self, T> {
        modifier(viewModifier)
    }
}

Usage

I use it with this extension:

extension View {
    func eraseToAnyView() -> AnyView { .init(self) }
}

And modifier declaration now looks like this:

extension _ViewModifier {

    // Declaration
    static func largeButton<T: View>() -> _ViewModifier<T, AnyView> {
        let size = CGSize(width: 300, height: 50)
        let fontModifier: CGFloat = 0.4
        return .init { content in
            content
                .font(.system(size: round(size.height * fontModifier), weight: .medium))
                .frame(
                    idealWidth: size.width,
                    maxWidth: .infinity,
                    idealHeight: size.height,
                    maxHeight: size.height
                )
                .eraseToAnyView()
        }
    }
    
}

// Usage
Button(action: someAction}) { Text("TapMe") }
    .modifier(.largeButton())

instead of this

// Declaration
struct LargeButtonModifier: ViewModifier {
    let size = CGSize(width: 300, height: 50)
    let fontModifier: CGFloat = 0.4
    func body(content: Content) -> some View {
        content
        .font(.system(size: round(size.height * fontModifier), weight: .medium))
        .frame(idealWidth: size.width, maxWidth: .infinity,
               idealHeight: size.height, maxHeight: size.height)
    }
}

// Usage
Button(action: someAction}) { Text("TapMe") }
    .modifier(LargeButtonModifier())

Back to index