From 4678d403c2dde7e577ada78df89d44d58dd10543 Mon Sep 17 00:00:00 2001
From: Thibault Wittemberg <twittemberg@genetec.com>
Date: Wed, 2 Feb 2022 20:23:28 +0100
Subject: [PATCH] operators: implement Assign

---
 README.md                                     | 15 ++++++++++
 Sources/Operators/AsyncSequence+Assign.swift  | 29 +++++++++++++++++++
 .../Operators/AsyncSequence+AssignTests.swift | 29 +++++++++++++++++++
 3 files changed, 73 insertions(+)
 create mode 100644 Sources/Operators/AsyncSequence+Assign.swift
 create mode 100644 Tests/Operators/AsyncSequence+AssignTests.swift

diff --git a/README.md b/README.md
index 0055444..a29375e 100644
--- a/README.md
+++ b/README.md
@@ -41,6 +41,7 @@ AsyncSequences
 * [SwitchToLatest](#SwitchToLatest)
 * [FlatMapLatest](#FlatMapLatest)
 * [HandleEvents](#HandleEvents)
+* [Assign](#Assign)
 * [EraseToAnyAsyncSequence](#EraseToAnyAsyncSequence)
 
 More operators and extensions are to come. Pull requests are of course welcome.
@@ -376,6 +377,20 @@ for try await element in handledSequence {}
 // finished
 ```
 
+### Assign
+
+`assign(to:on:)` assigns each element from the async sequence to a property on an object.
+
+```swift
+class Root {
+    var property: String = ""
+}
+
+let root = Root()
+let fromSequence = AsyncSequences.From(["1", "2", "3"])
+try await fromSequence.assign(to: \.property, on: root) // will set the property value to "1", "2", "3"
+```
+
 ### EraseToAnyAsyncSequence
 
 `eraseToAnyAsyncSequence()` type-erases the async sequence into an AnyAsyncSequence.
diff --git a/Sources/Operators/AsyncSequence+Assign.swift b/Sources/Operators/AsyncSequence+Assign.swift
new file mode 100644
index 0000000..eab683e
--- /dev/null
+++ b/Sources/Operators/AsyncSequence+Assign.swift
@@ -0,0 +1,29 @@
+//
+//  AsyncSequence+Assign.swift
+//  
+//
+//  Created by Thibault Wittemberg on 02/02/2022.
+//
+
+public extension AsyncSequence {
+    /// Assigns each element from the async sequence to a property on an object.
+    ///
+    /// ```
+    /// class Root {
+    ///     var property: String = ""
+    /// }
+    ///
+    /// let root = Root()
+    /// let fromSequence = AsyncSequences.From(["1", "2", "3"])
+    /// try await fromSequence.assign(to: \.property, on: root) // will set the property value to "1", "2", "3"
+    /// ```
+    ///
+    /// - Parameters:
+    ///   - keyPath: A key path that indicates the property to assign.
+    ///   - object: The object that contains the property.
+    func assign<Root>(to keyPath: ReferenceWritableKeyPath<Root, Self.Element>, on object: Root) async throws {
+        for try await element in self {
+            object[keyPath: keyPath] = element
+        }
+    }
+}
diff --git a/Tests/Operators/AsyncSequence+AssignTests.swift b/Tests/Operators/AsyncSequence+AssignTests.swift
new file mode 100644
index 0000000..9a84bf7
--- /dev/null
+++ b/Tests/Operators/AsyncSequence+AssignTests.swift
@@ -0,0 +1,29 @@
+//
+//  AsyncSequence+AssignTests.swift
+//  
+//
+//  Created by Thibault Wittemberg on 02/02/2022.
+//
+
+import AsyncExtensions
+import XCTest
+
+private class Root {
+
+    var successiveValues = [String]()
+
+    var property: String = "" {
+        didSet {
+            self.successiveValues.append(self.property)
+        }
+    }
+}
+
+final class AsyncSequence_AssignTests: XCTestCase {
+    func testAssign_sets_elements_on_the_root() async throws {
+        let root = Root()
+        let sut = AsyncSequences.From(["1", "2", "3"])
+        try await sut.assign(to: \.property, on: root)
+        XCTAssertEqual(root.successiveValues, ["1", "2", "3"])
+    }
+}