View+Assign.swift

//
//  View+Assign.swift
//  Created by Sean on 7/29/22.
//

import SwiftUI

// You cannot safely assign to a state variable during view update - such as inside the block of a GeometryReader.
// Rather than do an unsafe hack like DispatchQueue.main.async or resorting to a PreferenceKey or even Combine, we
// can simply defer the assignment to a time when it *is* safe to update State- such as inside of the task block!
// The only requirement here is that the value be Equatable. This ensures that we don't bother updating the binding
// unless the value *actually* changes which saves us time and can also prevent layout update loops. As an added
// bonus, we're using an autoclosure so that if no binding is supplied (your view might have an optional binding),
// the value need not even be computed in the first place. Much efficient. Very buttery. Such performance!

extension View {
    @ViewBuilder func assign<Value: Equatable>(_ value: @autoclosure ()->Value, to binding: Binding<Value>?) -> some View {
        if let binding {
            let computedValue = value()
            task(id: computedValue) {
                binding.wrappedValue = computedValue
            }
        } else {
            self
        }
    }
}