add iOS

iOS-SwiftUI-Code/GRDB.swift-6.29.3/GRDB/ValueObservation/Reducers/Fetch.swift

@@ -0,0 +1,20 @@
+extension ValueReducers {
+    /// A `ValueReducer` that perform database fetches.
+    public struct Fetch<Value>: ValueReducer {
+        private let __fetch: (Database) throws -> Value
+        
+        /// Creates a reducer which passes raw fetched values through.
+        init(fetch: @escaping (Database) throws -> Value) {
+            self.__fetch = fetch
+        }
+        
+        public func _fetch(_ db: Database) throws -> Value {
+            assert(db.isInsideTransaction, "Fetching in a non-isolated way is illegal")
+            return try __fetch(db)
+        }
+        
+        public func _value(_ fetched: Value) -> Value? {
+            fetched
+        }
+    }
+}