Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.14)
// Compass (v1.0.1)
// ----

@mixin imgHoverEffect ($selector: '.selector') {
  display: block;
  background: #fff;
  img{
    display: block;
    transition: opacity 0;
    #{$selector} & {
      opacity: .5;
      transition: opacity .2s;
    }
  }
}

.hoge {
  @include imgHoverEffect($selector:'.ie8');
}

SassMeister-output.css

.hoge{display:block;background:#fff}.hoge img{display:block;transition:opacity 0}.ie8 .hoge img{opacity:.5;transition:opacity .2s}