LESS CSS Variable based on variable - variables

Question

I'm using LESS to build a site, and want the layout to switch based on direction, either 'ltr' or 'rtl' (direction:rtl)
I set #direction at the top. Then there are certain elements that I want floated left for ltr, and right for rtl. I also want to position absolute, and apply padding-left/right based on the #direction.
Instead of writing out separate mixins for float, pos and padding, I was trying to do something like this:
.mixin (#direction) when (#direction = ltr) {
#lr:left;
}
.mixin (#direction) when (#direction = rtl) {
#lr:right;
}
Then call it like this:
ol li {
float:#lr;
}
and/or
ol li span.date {
position:absolute;
#lr:0;
}
That's the idea, but any help would be appreciated. I've looked at guards, and parametric mixins but just can't seem to nail it.

Answer 1

I have an idea for your case which solve RTL problem. In each class, we define 2 mixin within it for direction stylesheet properties. The prototype like that:
// #direction variable should be put by somehow
#direction: rlt;
.foo {
// common properties;
.dir(#direction);
.dir(rtl) {
// RTL properties;
}
.dir(ltr) {
// LTR properties;
}
}
For example:
// #direction variable should be put by somehow
#direction: rlt;
.foo {
color: #000000;
.dir(#direction);
.dir(rtl) {
float: left;
padding-left: 5px;
background: "rtl.png";
}
.dir(ltr) {
float: right;
padding-right: 5px;
background: "ltr.png";
}
}

Answer 2

OK. After some playing and a bit of thinking this is what I've come up with. If I can't use variables as properties then I'll use #direction, and #directionOpp (opposite of rtl, ltr) to use as a layout helper.
I have 2 variables.
#direction: ltr; // Change to 'rtl' for arabic, hebrew, etc.
#directionOpp: rtl; // Make this opposite of #direction, for easier mixins
Here's my mixin for horizontal positioning.
#dir {
.dir(ltr,#dist:0) {left: #dist;}
.dir(rtl,#dist:0) {right: #dist;}
.float(ltr){float:left; }
.float(rtl){float:right;}
.margin(ltr, #dist:#a){margin-left:#dist;}
.margin(rtl, #dist:#a){margin-right:#dist;}
.padding(ltr, #dist:#a){padding-left:#dist;}
.padding(rtl, #dist:#a){padding-right:#dist;}
}
and here's how I call it.
ol li {
#dir.float(#direction);
#dir.padding(#direction);
}
If I ever need to reverse anything, then I can replace #direction with #directionOpp.
I can also specifiy how much #dist I need as it's parametric mixin, and since they're all separate I can have any combination of margin, float, padding etc I need without multiple mixins with hard coded properties.
Good solution?
Dave

Answer 3

Your first issue is that variables are actually constants in LESS. So once you set it, it can not be overwritten. When you set #lr to "left", then it will always have "left" as its value, even if you try to reset the variable. Which is the issue with your first idea.
As far as your second idea, LESS does not support using variables as properties, only values. However you can hack around it like so:
.mixin(#prop, #value) {
Ignore: ~"a;#{prop}:#{value}";
}
This isn't very clean, but it does the trick if you absolutely need the functionality. Word is it is in the works for 1.4.
Also, you are calling the mixin incorrectly. Try something like this:
.mixin (#direction) when (#direction = ltr) {
float: left;
}
.mixin (#direction) when (#direction = rtl) {
float: right;
}
Then call it like this:
ol li {
.mixin(ltr);
}
Which should spit this out:
ol li {
float: left;
}

Answer 4

Try this Mixins in your LESS files
#rtl: rtl;
#ltr: ltr;
#direction: #rtl;
then Use them like this
html {
direction: #direction;
}
body{
direction: #direction;
}
for Left and Right commands you should use these mixins
.DockItem(#location, #value) when (#location = "left") and (#direction = #ltr){
left: #value;
}
.DockItem(#location, #value) when (#location = "right") and (#direction = #ltr){
right: #value;
}
.DockItem(#location, #value) when (#location = "left") and (#direction = #rtl){
right: #value;
}
.DockItem(#location, #value) when (#location = "right") and (#direction = #rtl){
left: #value;
}
then in your less file you should call this mixins like this
.TestClass{
.DockItem('left', '100%');
}
Note that I set #direction to RTL so above style would result like this
.TestClass{
right: 100%;
}
If you set chnage the directionality of the page to LTR it would result like this
.TestClass{
left: 100%;
}
Let me know if it helps you or not

Answer 5

I implemented a rtl extension in dotless. Find it on github. That extension reverwses float:left to float:right and margin-left:5px to margin-right:5px.
It also supports prefixing properties to control how they are reversed.
A lot more info is available on the dotless wiki for the plugin.
You can find generic information on how to use dotless and plugins also on the wiki.