add swiftUI code

2025-01-22 14:09:10 +08:00
parent 68e7b7347c
commit 8a99853829
2531 changed files with 486215 additions and 0 deletions
@@ -0,0 +1,53 @@
+extension ValueObservation {
+    /// Transforms all values from the upstream observation with a
+    /// provided closure.
+    ///
+    /// For example:
+    ///
+    /// ```swift
+    /// // Turn an observation of Player? into an observation of UIImage?
+    /// let observation = ValueObservation
+    ///     .tracking { db in try Player.fetchOne(db, id: 42) }
+    ///     .map { player in player?.image }
+    /// ```
+    ///
+    /// The `transform` closure does not run on the main thread, and does not
+    /// block any database access This makes the `map` operator a tool that
+    /// helps reducing database contention
+    /// (see <doc:ValueObservation#ValueObservation-Performance>).
+    ///
+    /// - parameter transform: A closure that takes one value as its parameter
+    ///   and returns a new value.
+    public func map<T>(_ transform: @escaping (Reducer.Value) throws -> T)
+    -> ValueObservation<ValueReducers.Map<Reducer, T>>
+    {
+        mapReducer { ValueReducers.Map($0, transform) }
+    }
+}
+
+extension ValueReducers {
+    /// A `ValueReducer` whose values consist of those in a `Base` reduced
+    /// passed through a transform function.
+    ///
+    /// See ``ValueObservation/map(_:)``.
+    public struct Map<Base: _ValueReducer, Value>: _ValueReducer {
+        private var base: Base
+        private let transform: (Base.Value) throws -> Value
+        
+        init(_ base: Base, _ transform: @escaping (Base.Value) throws -> Value) {
+            self.base = base
+            self.transform = transform
+        }
+        
+        public mutating func _value(_ fetched: Base.Fetched) throws -> Value? {
+            guard let value = try base._value(fetched) else { return nil }
+            return try transform(value)
+        }
+    }
+}
+
+extension ValueReducers.Map: ValueReducer where Base: ValueReducer {
+    public func _fetch(_ db: Database) throws -> Base.Fetched {
+        try base._fetch(db)
+    }
+}