FirstNonNil<T>

📦 irstNonNil

// 2020.10.15：

import SwiftUI

// 📦 FirstNonNil<T>
public struct FirstNonNil<T>: PreferenceKey {
    public typealias Value = T?
    // default value
    public static var defaultValue: Value { nil }
    // combine values from different child views
    public static func reduce(value: inout Value, nextValue: () -> Value) {
        value = value ?? nextValue()   // nil or first non-nil value
    }
}

👥 相關

• 🅿️ PreferenceKey