Sass Mixin Parameter - Stop Sass from converting Fraction (e.g. 1/3 converts to 0.33333)?

Question

Situation

I have a Mixin like this:

@mixin column($fraction: null) {
    // ...do stuff with $fraction
}

It can be used like so:

@include column('1/3');

Please note:

1. A String is passed
2. I need the denominator (3) to do some nth-child magic.

This works (used str-index + str-slice).

Problem

Now I'd like to make the quotes optional.
Meaning, this also needs to work:

@include column(1/3); // no quotes

Sass treats this as a number. Thats fine.
But it always does a division before I can do anything with the variable .

Example

Include:

@include column(1/3);

Mixin:

@mixin column($fraction: null) {
    $myVar: $fraction // $fraction equals '0.3333333' at this point already
}

Is there a way to prevent Sass from doing that? Or another way to get the denominator?

Thanks!

---

Additional Notes

About using a Comma instead of Slash

As proposed by @Johannes Reuter I could just use a comma instead of a slash:

@include column(1,3);

Unfortunately means that the include looses a bit of meaning.
With a "1/3" it's clear that the column will be one third in width. I'd like to keep that.

It especially gets confusing with more parameters:

@include column(1, 3, 3, stacking);

vs

@include column(1/3, 3, stacking);

But thanks a lot for this answer.

Answer 1

You could pass the numerator and the denominator as two separate parameters:

Include:

@include column(1,3);

Mixin:

@mixin column($numerator: null, $denominator: null) {
 //...
}

This would be much cleaner than string-operations.

Answer 2

Is a dirty trick but if you use argument list you get the value without division, then you have to convert in to string for extract the second value with str-slice :

SASS

@mixin column($fraction...) {
  $fraction: $fraction + "";
  $n:str-slice($fraction, 3);
  &:nth-child(#{$n}){
    display:block;
  }
}

.class{
  @include column(1/3);
}

OUTPUT

.class:nth-child(3) {
  display: block;
}

PS: The problem is if you want to use more parameters. I don't know how to solve it.

---

UPDATE 28/09/2016

I found a way to do with two mixins, one with a list of parameters and the css properties and another one with variable arguments where I extract the number after division operator.

Variable arguments prevents doing the division but all the parameter go together and if I extract the 1st parameter the division doing again. Using two diferent mixins I can use the variable arguments and at the same time maintain separate parameters:

SASS

 @mixin column2($col, $gutter) { width: $col * 100%; padding: $gutter; } @mixin column($args...) { $args-str: inspect($args); $separator: str-index($args-str, ","); $separator2: str-index($args-str, "/"); $fraction: str-slice($args-str, 1, $separator - 1); $cols: unquote(str-slice($fraction, $separator2 + 1)); &:nth-child(#{$cols}){ @include column2($args...); } } .class { @include column(1/3, 3px); } 

OUTPUT

 .class:nth-child(3) { width: 33.33333%; padding: 3px; }