1回だけ更新可能、1回だけ実行可能

OnceExecutable.swift

import Foundation

@propertyWrapper
class OnceExecutable {
    @OnceUpdatable
    private var execute: () -> Void
    private var isExecuted = false
    
    var wrappedValue: () -> Void {
        get { execute }
        set {
            execute = {
                guard !self.isExecuted else {
                    assertionFailure("can't execute twice!")
                    return
                }
                self.isExecuted = true
                newValue()
            }
        }
    }
    
    init(wrappedValue: @escaping () -> Void = {}) {
        execute = wrappedValue
    }
}

OnceUpdatable.swift

import Foundation

@propertyWrapper
struct OnceUpdatable<Value> {
    private var value: Value
    private var maxUpdatableCount = 1
    private var updatedCount = 0
    
    var wrappedValue: Value {
        get { value }
        set {
            guard updatedCount < maxUpdatableCount else {
                assertionFailure("can't update any more!")
                return
            }
            updatedCount += 1
            value = newValue
        }
    }
    
    init(wrappedValue: Value, maxUpdatableCount: Int = 1) {
        value = wrappedValue
        self.maxUpdatableCount = maxUpdatableCount
    }
}