LifetimeTask and ThrowingLifetimeTask modifiers

LifetimeTask.swift

import SwiftUI

private struct LifetimeTask: ViewModifier {
  @State @Reference private var hasAppeared = false
  @State @Reference private var task: Task<Void, Never>?
  let perform: () async -> Void

  func body(content: Content) -> some View {
    content
      .onFirstAppear {
        task = Task {
          await perform()
        }
      }
      .onDestroy {
        task?.cancel()
      }
  }
}

public extension View {
  func lifetimeTask(perform: @escaping () async -> Void) -> some View {
    self.modifier(LifetimeTask(perform: perform))
  }
}

private struct ThrowingLifetimeTask: ViewModifier {
  @State @Reference private var hasAppeared = false
  @State @Reference private var task: Task<Void, Never>?
  @Environment(\.[service: \Throw.self]) private var `throw`
  let perform: () async throws -> Void

  func body(content: Content) -> some View {
    content
      .onFirstAppear {
        task = `throw`.try {
          try await perform()
        }
      }
      .onDestroy {
        task?.cancel()
      }
  }
}

public extension View {
  func throwingLifetimeTask(perform: @escaping () async throws -> Void) -> some View {
    self.modifier(ThrowingLifetimeTask(perform: perform))
  }
}

// MARK: OnFirstAppear and OnDestroy helpers
// We shouldn't need to use these in client code, so they're fileprivate.

private struct OnFirstAppear: ViewModifier {
  @State @Reference private var hasAppeared = false
  var perform: () -> Void
  func body(content: Content) -> some View {
    content
      .onAppear {
        guard !hasAppeared else { return }
        hasAppeared = true
        perform()
      }
  }
}

fileprivate extension View {
  func onFirstAppear(perform: @escaping () -> Void) -> some View {
    self.modifier(OnFirstAppear(perform: perform))
  }
}

private struct OnDestroy: ViewModifier {
  let onDestroy: () -> Void
  final class Lifetime {
    var onDestroy: () -> Void = { }
    deinit { onDestroy() }
  }
  @State var lifetime: Lifetime = .init()
  func body(content: Content) -> some View {
    lifetime.onDestroy = onDestroy
    return content
      .background(Color.clear) //this needs to be actually different than content itself, else `body(content:)` wont even run (thanks to SwiftUI magic)
  }
}

fileprivate extension View {
  func onDestroy(_ onDestroy: @escaping () -> Void) -> some View {
    self.modifier(OnDestroy(onDestroy: onDestroy))
  }
}