Add join() for attribute functions.

Author: natestedman

Attributed/AttributedStringConvertible.swift

@@ -10,6 +10,11 @@
 
 import Foundation
 
+// MARK: - Function Types
+
+/// An attribute function.
+public typealias AttributeFunction = [AttributedStringConvertible] -> AttributedStringConvertible
+
 // MARK: - Protocol
 
 /// A protocol for a type that can be converted to an attributed string.

Attributed/SequenceType+Join.swift

@@ -18,3 +18,17 @@ public extension SequenceType where Generator.Element == AttributedStringConvert
         return NestedAttributedString(attributes: [:], children: Array(self))
     }
 }
+
+public extension SequenceType where Generator.Element == AttributeFunction
+{
+    /// Joins a sequence of partially applied attribute functions (or, extension member functions of an attribute value)
+    /// into a single function.
+    ///
+    /// If redundant attributes are included, the later version will take precedence.
+    public func join() -> AttributeFunction
+    {
+        return { strings in
+            self.reverse().reduce(strings.join(), combine: { current, function in function([current]) })
+        }
+    }
+}

AttributedTests/AttributedTests.swift

@@ -77,7 +77,7 @@ class AttributedTests: XCTestCase
         XCTAssertEqual(attributed, mutable)
     }
 
-    func testJoin()
+    func testStringJoin()
     {
         let attributed = [
             "Test",
@@ -89,4 +89,39 @@ class AttributedTests: XCTestCase
 
         XCTAssertEqual(attributed, mutable)
     }
+    
+    func testFunctionJoin()
+    {
+        let functions = [
+            ColorType.blackColor().foregroundAttribute,
+            ColorType.redColor().backgroundAttribute,
+            2.kernAttribute
+        ]
+        
+        XCTAssertEqual(
+            functions.join()(["Test"]).attributedString,
+            NSAttributedString(
+                string: "Test",
+                attributes: [
+                    NSForegroundColorAttributeName: ColorType.blackColor(),
+                    NSBackgroundColorAttributeName: ColorType.redColor(),
+                    NSKernAttributeName: 2
+                ]
+            )
+        )
+    }
+    
+    func testFunctionJoinOverride()
+    {
+        let functions = [
+            ColorType.redColor().foregroundAttribute,
+            ColorType.greenColor().foregroundAttribute,
+            ColorType.blueColor().foregroundAttribute,
+        ]
+        
+        XCTAssertEqual(
+            functions.join()(["Test"]).attributedString,
+            NSAttributedString(string: "Test", attributes: [NSForegroundColorAttributeName: ColorType.blueColor()])
+        )
+    }
 }