add x= and /= to extends values

docs/layouts.rst

@@ -117,8 +117,10 @@ You can also **modify** data as they get passed through extends::
 The following operators are supported within evaluating ``extends``
   * ``+=`` will add the giuven number to the inherited number
   * ``-=`` will subtract the given number from the inherited number
+  * ``x=`` will multiply the inherited number by the given number
+  * ``/=`` will divide the inherited number by the given number
 
-Both operators also support :doc:`/units`
+``+=`` and ``-=`` also support :doc:`/units`
 
 From a design point of view, you can also extract out a base design and have your other layouts extend from them::
 
@@ -149,10 +151,10 @@ As you might expect, ``extends`` can be composed multiple times::
     x: 100
   plato:
     extends: socrates
-    x: += 10    # evaluates to 150
+    x: += 10    # evaluates to 110
   aristotle:
     extends: plato
-    x: += 20    # evaluates to 150
+    x: x= 2     # evaluates to 220
 
 Yes, ``extends`` has Multiple Inheritance
 -----------------------------------------
@@ -167,7 +169,7 @@ If you want to extend multiple parents, it looks like this::
     extends:
       - socrates
       - plato
-    x: += 50    # evaluates to 150
+    x: += 50    # evaluates to 250 from plato
 
 If multiple keys override the same keys in a parent, the later ("younger") child in the ``extends`` list takes precedent. Like this::
 

lib/squib/layout_parser.rb

@@ -53,6 +53,10 @@ module Squib
             add_parent_child(parent_val, child_val)
           elsif child_val.to_s.strip.start_with?('-=')
             sub_parent_child(parent_val, child_val)
+          elsif child_val.to_s.strip.start_with?('x=')
+            mul_parent_child(parent_val, child_val)
+          elsif child_val.to_s.strip.start_with?('/=')
+            div_parent_child(parent_val, child_val)
           else
             child_val # child overrides parent when merging, no +=
           end
@@ -76,6 +80,18 @@ module Squib
       parent_pixels - child_pixels
     end
 
+    def mul_parent_child(parent, child)
+      parent_pixels = Args::UnitConversion.parse(parent, @dpi).to_f
+      child_float = child.sub('x=', '').to_f
+      parent_pixels * child_float
+    end
+
+    def div_parent_child(parent, child)
+      parent_pixels = Args::UnitConversion.parse(parent, @dpi).to_f
+      child_float = child.sub('/=', '').to_f
+      parent_pixels / child_float
+    end
+
     # Does this layout entry have an extends field?
     # i.e. is it a base-case or will it need recursion?
     # :nodoc: