Sass helper function to get the block in the current selector

_bem-block.scss

@function b() {
  $selector: str-slice(inspect(&), 2, -2);
  @each $type in '__', '--' {
    @if str-index($selector, $type) {
      $selector: str-slice($selector, 0, str-index($selector, $type) - 1);
    }
  }
  @return $selector;
}

.media {
  border: 1px solid;
  &__content {
    font-size: 10px;
  }
  &--large {
    #{b()}__content {
      font-size: 20px;
    }
  }
}

output.css

.media {
  border: 1px solid;
}
.media__content {
  font-size: 10px;
}
.media--large .media__content {
  font-size: 20px;
}