[TSCUtility] Add some helpers for Context

Author: aciidgh

Diff for: Sources/TSCUtility/Context.swift

@@ -12,3 +12,26 @@ import Foundation
 
 /// Typealias for an any typed dictionary for arbitrary usage to store context.
 public typealias Context = [ObjectIdentifier: Any]
+
+extension Context {
+    /// Get the value for the given type.
+    public func get<T>(_ type: T.Type = T.self) -> T {
+        guard let value = getOptional(type) else {
+            fatalError("no type \(T.self) in context")
+        }
+        return value
+    }
+
+    /// Get the value for the given type, if present.
+    public func getOptional<T>(_ type: T.Type = T.self) -> T? {
+        guard let value = self[ObjectIdentifier(T.self)] else {
+            return nil
+        }
+        return value as! T
+    }
+
+    /// Set a context value for a type.
+    public mutating func set<T>(_ value: T) {
+        self[ObjectIdentifier(T.self)] = value
+    }
+}

Diff for: Tests/TSCUtilityTests/ContextTests.swift

@@ -0,0 +1,26 @@
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+
+import XCTest
+
+import TSCUtility
+
+struct SomeType {
+    var name: String
+}
+
+class ContextTests: XCTestCase {
+    func testBasics() {
+        var ctx = Context()
+        ctx.set(SomeType(name: "test"))
+        XCTAssertEqual(ctx.get(SomeType.self).name, "test")
+
+        ctx.set(SomeType(name: "optional"))
+        XCTAssertEqual(ctx.getOptional(SomeType.self)?.name, "optional")
+    }
+}