67 lines
1.9 KiB
Swift
67 lines
1.9 KiB
Swift
// Copyright 2022 Tokamak contributors
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 (the "License");
|
|
// you may not use this file except in compliance with the License.
|
|
// You may obtain a copy of the License at
|
|
//
|
|
// http://www.apache.org/licenses/LICENSE-2.0
|
|
//
|
|
// Unless required by applicable law or agreed to in writing, software
|
|
// distributed under the License is distributed on an "AS IS" BASIS,
|
|
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
// See the License for the specific language governing permissions and
|
|
// limitations under the License.
|
|
//
|
|
// Created by Carson Katri on 2/3/22.
|
|
//
|
|
|
|
/// A type that can visit a `View`.
|
|
public protocol ViewVisitor {
|
|
func visit<V: View>(_ view: V)
|
|
}
|
|
|
|
public extension View {
|
|
func _visitChildren<V: ViewVisitor>(_ visitor: V) {
|
|
visitor.visit(body)
|
|
}
|
|
}
|
|
|
|
public typealias ViewVisitorF<V: ViewVisitor> = (V) -> ()
|
|
|
|
/// A type that creates a `Result` by visiting multiple `View`s.
|
|
protocol ViewReducer {
|
|
associatedtype Result
|
|
static func reduce<V: View>(into partialResult: inout Result, nextView: V)
|
|
static func reduce<V: View>(partialResult: Result, nextView: V) -> Result
|
|
}
|
|
|
|
extension ViewReducer {
|
|
static func reduce<V: View>(into partialResult: inout Result, nextView: V) {
|
|
partialResult = Self.reduce(partialResult: partialResult, nextView: nextView)
|
|
}
|
|
|
|
static func reduce<V: View>(partialResult: Result, nextView: V) -> Result {
|
|
var result = partialResult
|
|
Self.reduce(into: &result, nextView: nextView)
|
|
return result
|
|
}
|
|
}
|
|
|
|
/// A `ViewVisitor` that uses a `ViewReducer`
|
|
/// to collapse the `View` values into a single `Result`.
|
|
final class ReducerVisitor<R: ViewReducer>: ViewVisitor {
|
|
var result: R.Result
|
|
|
|
init(initialResult: R.Result) {
|
|
result = initialResult
|
|
}
|
|
|
|
func visit<V>(_ view: V) where V: View {
|
|
R.reduce(into: &result, nextView: view)
|
|
}
|
|
}
|
|
|
|
extension ViewReducer {
|
|
typealias Visitor = ReducerVisitor<Self>
|
|
}
|