tl;dr Somebody discovered the power of mixins
I don't see how SASS is doing something unique here that other preprocessors can't do as well.
I don't see how SASS is doing something unique here that other preprocessors can't do as well.
It's not unique, but it has been an awfully long time coming. See: https://github.com/nex3/sass/pull/236
.media() { // won't compile directly width: 100%; // other cool styling }
img { .media; }
which would output just
img { width: 100%; }
Gives me similar results I think or am I missing something?
And the point is even @extend can get bloaty when nested, but placeholder tags avoid that problem, and remove the extra pattern classes from the output.
So the article is actually advocating that you stop using mixins. Mixins aren't OOCSS, they're just copy and paste made easier.
I'm actually working on a css post-processor script that optimizes css output. Grouping styles in the most efficient way possible is quite tricky.
This didn't come through entirely until I read the comment. I think an example of what mixins would produce would be helpful.
At the end of the day we have two goals: 1) keeping things easy to develop and 2) keeping the CSS filesize as small as possible.
Mixins accomplished 1 but not 2.
One potentially relevant example is bootstrap's core "btn" class, which has over 50 lines: https://github.com/twitter/bootstrap/blob/master/less/button...
When you want a button in HTML you have to add the btn class, as well as an additional class for that button's styling. IE: btn-large, btn-primary, btn-info
Bootstrap could have made this happen with just one class by implementing mixins, but that would result in each btn-primary, btn-info, etc repeating those 50 lines from the btn class.
If Bootstrap used @extend instead, that large btn class could be replaced with a multiple selector, IE: .btn-large, .btn-small, .btn-primary, etc. Then the independent styles could be defined below, as they already are, and we would just need one class to add the appropriate button style.
I guess they could do that today by just using the long selector instead of .btn, but that makes the file harder to maintain.
Let me know if I'm thinking about this wrong.
The example also combines hr {/* style /} .separator {/ style /} into one selector hr, .separator {/ style */}
but maybe that is something a CSS minifier should be able to do?
But it also used to annoy me how much it was overlooked. Not for Sass so much, but LESS is horrible compared to either Sass or Stylus.
That being said, Stylus doesn't have the ability to extend selectors that don't appear in markup, the way @extend'ing %placeholders works in Sass. (Not that I blame TJ, the guy's awesome repo ratio is the best on github!)
The thing that gets me frustrated with both Stylus and Jade is that they go a bit too far in the minimal syntax direction at the cost of other syntax improvements (since going minimal means its harder to differentiate pieces). The Sass syntax is more than simple enough, and the option to drop semi-colons is a cool thought experiment, but not so useful in real scenarios.
And then there's momentum too. I mostly just wish that we could all get behind one pre-processor, and Sass is the one with the best momentum. (I say best, because LESS has some momentum, but it's syntax is way less thought through, and it has less active committers.) I don't blame TJ at all for this, but he definitely has less time to devote to Stylus than the multiple Sass contributors do. Mostly it's just a question of putting your chips with the player with the most momentum because that will bring you the fastest updates.
In many ways, it seems like placeholders would almost always be preferred to mixins. Though, I'm sure there are exceptions.