SASS equivalent to LESS Space ("+_") syntax - sass

Question

LESS has a great little feature called Space that allows mixins to append rules to existing properties. Really useful for transform() mixins, because you can append many transform rules to the same property, just by calling the mixin multiple times, eg.
Example:
.scale() {
transform+_: scale(2);
}
.rotate() {
transform+_: rotate(15deg);
}
.myclass {
.scale();
.rotate();
}
Outputs:
.myclass {
transform: scale(2) rotate(15deg);
}
I'm trying to get into SASS, but I don't understand how to achieve this with the available syntax. Whatever I do, the output only ever applies one of the transformations, not both. What is the best way to achieve this behaviour using SASS alone?

Answer 1

You can use variable arguments in a mixin like so:
#mixin transform($transforms...) {
transform: $transforms;
}
.myclass {
#include transform(scale(0.5) rotate(30deg));
}
this will output:
.myclass {
transform: scale(0.5) rotate(30deg);
}
You can see a working example here:
http://codepen.io/sonnyprince/pen/RaMzgb
A little more info:
Sometimes it makes sense for a mixin or function to take an unknown
number of arguments. For example, a mixin for creating box shadows
might take any number of shadows as arguments. For these situations,
Sass supports “variable arguments,” which are arguments at the end of
a mixin or function declaration that take all leftover arguments and
package them up as a list. These arguments look just like normal
arguments, but are followed by ....
http://sass-lang.com/documentation/file.SASS_REFERENCE.html#variable_arguments

Answer 2

Sass does not offer such a feature.
You can get reasonably close by using global variables. However, every single mixin you use, including ones provided by a 3rd party, will have to be modified to work this way.
// the setup
$append-property-vals: (); // global variable
$old-append-property-vals: (); // global variable
#mixin append-property($key, $val, $separator: comma) {
$old-val: map-get($append-property-vals, $key);
#if $old-val {
$append-property-vals: map-merge($append-property-vals, ($key: append($old-val, $val, $separator))) !global;
} #else {
$append-property-vals: map-merge($append-property-vals, ($key: $val)) !global;
}
}
#mixin append-properties {
// cache the original value
$old-append-property-vals: $append-property-vals !global;
#content;
// write out the saved up properties
#each $key, $val in $append-property-vals {
#{$key}: $val;
}
// restore the original value
$append-property-vals: $old-append-property-vals !global;
}
// modify the OP's provided mixins to work
#mixin scale {
// if the vals should be comma delimited, write `comma` instead of `space` for the 3rd argument
#include append-property(transform, scale(2), space);
}
#mixin rotate {
#include append-property(transform, rotate(15deg), space);
}
// call the mixins
.myclass {
#include append-properties {
#include scale;
#include rotate;
}
}
Output:
.myclass {
transform: scale(2) rotate(15deg);
}