SASS micro clearfix mixin http://nicolasgallagher.com/micro-clearfix-hack/#comment-29398

micro-clearfix-mixin.scss

@mixin clearfix-micro() {
    & {
        *zoom: 1;
    }
    &:before,
    &:after {
        content: "";
        display: table;
    }
    &:after {
        clear: both;
    }
}

//Usage:
.whatever {
     @include clearfix-micro();
}

As no arguments are passed, are you sure you need a mixin? Have you considered the use of @extend?

I tried it with @extend and it ended badly. It doesn't work inside a media query in ruby sass and works very wrongly in libsass. Just a heads up!

If you need it for IE9+ you can use:

@mixin clearfix {
  &::after {
    clear: both;
    content: "";
    display: table;
  }
}

source: bourbon