Implement attribute(atIndex:effectiveRange:)

Author: eyeplum

Foundation/NSAttributedString.swift

@@ -76,7 +76,25 @@ public class NSAttributedString : NSObject, NSCopying, NSMutableCopying, NSSecur
         return CFAttributedStringGetLength(_cfObject)
     }
 
-    public func attribute(_ attrName: String, atIndex location: Int, effectiveRange range: NSRangePointer) -> AnyObject? { NSUnimplemented() }
+    public func attribute(_ attrName: String, atIndex location: Int, effectiveRange range: NSRangePointer) -> AnyObject? {
+        var cfRange = CFRange()
+        return withUnsafeMutablePointer(&cfRange) { (rangePointer: UnsafeMutablePointer<CFRange>) -> AnyObject? in
+            // Get attribute value using CoreFoundation function
+            let attribute = CFAttributedStringGetAttribute(_cfObject, location, attrName._cfObject, rangePointer)
+            
+            // Update effective range and return the result
+            if let attribute = attribute {
+                range.pointee.location = rangePointer.pointee.location
+                range.pointee.length = rangePointer.pointee.length
+                return attribute
+            } else {
+                range.pointee.location = NSNotFound
+                range.pointee.length = 0
+                return nil
+            }
+        }
+    }
+    
     public func attributedSubstringFromRange(_ range: NSRange) -> NSAttributedString { NSUnimplemented() }
 
     public func attributesAtIndex(_ location: Int, longestEffectiveRange range: NSRangePointer, inRange rangeLimit: NSRange) -> [String : AnyObject] { NSUnimplemented() }

TestFoundation/TestNSAttributedString.swift

@@ -39,6 +39,11 @@ class TestNSAttributedString : XCTestCase {
         XCTAssertEqual(range.location, NSNotFound)
         XCTAssertEqual(range.length, 0)
         XCTAssertEqual(attrs.count, 0)
+
+        let attribute = attrString.attribute("invalid", atIndex: 0, effectiveRange: &range)
+        XCTAssertNil(attribute)
+        XCTAssertEqual(range.location, NSNotFound)
+        XCTAssertEqual(range.length, 0)
     }
 
     func test_initWithStringAndAttributes() {
@@ -51,15 +56,27 @@ class TestNSAttributedString : XCTestCase {
 
         var range = NSRange()
         let attrs = attrString.attributesAtIndex(0, effectiveRange: &range)
-        
         guard let value = attrs["attribute.placeholder.key"] as? NSString else {
             XCTAssert(false, "attribute value not found")
             return
         }
-        
         XCTAssertEqual(range.location, 0)
         XCTAssertEqual(range.length, attrString.length)
         XCTAssertEqual(value, "attribute.placeholder.value")
+
+        let invalidAttribute = attrString.attribute("invalid", atIndex: 0, effectiveRange: &range)
+        XCTAssertNil(invalidAttribute)
+        XCTAssertEqual(range.location, NSNotFound)
+        XCTAssertEqual(range.length, 0)
+
+        let attribute = attrString.attribute("attribute.placeholder.key", atIndex: 0, effectiveRange: &range)
+        XCTAssertEqual(range.location, 0)
+        XCTAssertEqual(range.length, attrString.length)
+        guard let validAttribute = attribute as? NSString else {
+            XCTAssert(false, "attribuet not found")
+            return
+        }
+        XCTAssertEqual(validAttribute, "attribute.placeholder.value")
     }
 
 }