Conditional parameter validation in a LESS mixin function

Question

How can I translate the following conditional to LESS?

.mixin(@width) {
    width: (!@width ? auto : @width);
}

Results should be like:

[no value is passed]
LESS: .mixin();
CSS: width: auto;

[value is passed]
LESS: .mixin(200px);
CSS: width: 200px;

Answer 1

You can use default parameter values to accomplish this:

.mixin(@width: auto) {
  width: @width;
}