Generated by SassMeister.com.

SassMeister-input.sass

// ----
// libsass (v3.0)
// ----

// Mixins
@mixin extend($class:'&') {
  @if ($class != '&') {
    .#{$class} {
      @content
    }
  } @else {
    & {
      @content
    }
  }
}

// Demo
.link {
  text-decoration: underline;

  @include extend() {
    color: white;
    background :red;
  }
}

.pivo {
  background: black;
  
  &:first-child {
    color: pink;
  }
}

@include extend('pivo') {
  display: block;
  
  &:last-child {
    display: none;
  }
}

SassMeister-output.css

.link {
  text-decoration: underline; }
  .link {
    color: white;
    background: red; }

.pivo {
  background: black; }
  .pivo:first-child {
    color: pink; }

.pivo {
  display: block; }
  .pivo:last-child {
    display: none; }