New sass function: if

doc-src/SASS_CHANGELOG.md

@@ -6,6 +6,9 @@
 ## 3.2.0 (Unreleased)
 
 * Add an {Sass::Script::Functions#invert `invert` function} that takes the inverse of colors.
+* A new sass function called `if` can be used to emit one of two values
+  based on the truth value of the first argument. E.g. `if(true, 1px, 2px)`
+  returns `1px` and `if(false, 1px, 2px)` returns `2px`
 
 ### Backwards Incompatibilities -- Must Read!
 

lib/sass/script/functions.rb

@@ -825,6 +825,22 @@ def abs(value)
       numeric_transformation(value) {|n| n.abs}
     end
 
+    # returns one of two values based on the truth value of the first argument.
+    #
+    # @example
+    #   if(true, 1px, 2px) => 1px
+    #   if(false, 1px, 2px) => 2px
+    # @param truth [Bool] the expression to be evaluated for truth
+    # @param if_true will be returned if the truth value is true.
+    # @param if_false will be returned if the truth value is false.
+    def if(truth, if_true, if_false)
+      if truth.to_bool
+        if_true
+      else
+        if_false
+      end
+    end
+
     private
 
     # This method implements the pattern of transforming a numeric value into

test/sass/functions_test.rb

@@ -545,6 +545,11 @@ def test_comparable
     assert_error_message("#ff0000 is not a number for `comparable'", "comparable(1px, #f00)")
   end
 
+  def test_if
+    assert_equal("1px", evaluate("if(true, 1px, 2px)"))
+    assert_equal("2px", evaluate("if(false, 1px, 2px)"))
+  end
+
   private
 
   def evaluate(value)