Adding support for the animator proxy on OS X

@@ -165,6 +165,22 @@
     return self;
 }
 
+#pragma mark - Animator proxy
+
+#if TARGET_OS_MAC && !TARGET_OS_IPHONE
+
+- (id<MASConstraint>)animator
+{
+    for (id<MASConstraint> constraint in self.childConstraints) {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunused-value"
+        constraint.animator;
+#pragma clang diagnostic pop
+    }
+    return self;
+}
+#endif
+
 #pragma mark - debug helpers
 
 - (id<MASConstraint> (^)(id))key {

@@ -113,6 +113,13 @@
  */
 @property (nonatomic, copy, readonly) id<MASConstraint> (^key)(id key);
 
+#if TARGET_OS_MAC && !TARGET_OS_IPHONE
+/**
+ *  Whether or not to go through the animator proxy when modifying the constraint
+ */
+@property (nonatomic, copy, readonly) id<MASConstraint> animator;
+#endif
+
 /**
  *  Whether or not to check for an existing constraint instead of adding constraint
  */

@@ -22,6 +22,7 @@
 @property (nonatomic, assign) CGFloat layoutConstant;
 @property (nonatomic, assign) BOOL hasLayoutRelation;
 @property (nonatomic, strong) id mas_key;
+@property (nonatomic, assign) BOOL useAnimator;
 
 @end
 
@@ -57,7 +58,16 @@
 
 - (void)setLayoutConstant:(CGFloat)layoutConstant {
     _layoutConstant = layoutConstant;
+
+#if TARGET_OS_MAC && !TARGET_OS_IPHONE
+    if(self.useAnimator) {
+        self.layoutConstraint.animator.constant = layoutConstant;
+    } else {
+        self.layoutConstraint.constant = layoutConstant;
+    }
+#else
     self.layoutConstraint.constant = layoutConstant;
+#endif
 }
 
 - (void)setLayoutRelation:(NSLayoutRelation)layoutRelation {
@@ -247,6 +257,18 @@
     return self;
 }
 
+#pragma mark - Animator proxy
+
+#if TARGET_OS_MAC && !TARGET_OS_IPHONE
+
+- (id<MASConstraint>)animator
+{
+    self.useAnimator = YES;
+    return self;
+}
+
+#endif
+
 #pragma mark - debug helpers
 
 - (id<MASConstraint> (^)(id))key {