LazyState

LazyState.swift

//
//  LazyState.swift
//  Extensions
//
//  Created by Michael Long on 3/5/25.
//

import Observation
import SwiftUI

@MainActor
@propertyWrapper
public struct LazyState<T: Observable>: DynamicProperty {

    @State private var thunkedValue: ThunkedValue<T>

    public init(wrappedValue thunk: @autoclosure @escaping () -> T) {
        _thunkedValue = State(wrappedValue: ThunkedValue(wrappedValue: thunk))
    }

    public var wrappedValue: T {
        thunkedValue.value
    }

    public var projectedValue: Binding<T> {
        Binding(get: { thunkedValue.value }, set: { _ in })
    }

}

private final class ThunkedValue<T: Observable> {

    private var object: T!
    private var thunk: (() -> T)?

    init(wrappedValue thunk: @escaping () -> T) {
        self.thunk = thunk
    }

    var value: T {
        if let thunk {
            object = thunk()
            self.thunk = nil
        }
        return object
    }

}