Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.6)
// Compass (v1.0.1)
// ----

@mixin size($size) {
  $height: nth($size, 1);
  $width: $height;
  @if length($size) > 1 {
    $height: nth($size, 2);
  }
  @if $height == auto or (type-of($height) == number and not unitless($height)) {
    height: $height;
  }
  @if $width == auto or (type-of($width) == number and not unitless($width)) {
    width: $width;
  }
}

$height:10;

.sample {
  @include size(10px $height + px)
}

SassMeister-output.css

.sample {
  width: 10px;
}