null string for compiling

[kbdsbx]

/* making .display-block */
.make-classes () {
    @item : ~"";
    .make-classes( @item );
}

/* making .xs-display-block */
.make-classes ( @class ) when ( iskeyword( @class ) ) {
    @item : ~"@{class}-";
    .make-classes( @item );
}

/* inner function */
.make-classes ( @class ) when ( isstring( @class ) ) {
    .@{class}display-block { display: block; }
}

.make-classes ();

.make-classes( xs );

If I want to taking .display-block into some class as :

.shi {
    .display-block;
}

it will be tell me

NameError: .display-block is undefined on line 21, column 5:

but if I using .xs-display-block

.shi {
    .xs-display-block;
}

It's works.

so... Is that the null string are not supporting when compiling?

[SomMeri]

Interpolated rulesets (e.g. .@{class}display-block) should not work as mixins (see #1196 and #1338 for related issue).

Theoretically, neither .xs-display-block nor .display-block call should be working. But, it is interesting that this works too.

[seven-phases-max]

Theoretically, neither .xs-display-block nor .display-block call should be working.

They should per #1624 (so this is basically a bug in #1624).

---

Regardless of the error one should avoid such code (to be honest by these days I suppose that was a mistake to implement this feature at all). If one needs a parametric mixin she just uses parametric mixin (note in .shi both void and xs are nothing but parameters for a whatever mixin with one parameter) ``. Ideally (for manageable and solid code) parametric mixins must never be emulated via CSS classes (despite Less partially allowing you to do so via combination of certain features, i.e. "selector interpolation" + "interpolated-classes-as-mixin"). For more details and examples see #2702.