Sass Interpolation of Mixin, Function, and Variable names - sass

Question

I'm trying to loop through a list of values in Sass and use interpolation of the current key to dynamically output class names that utilize #include and #extend, respectively.
Here is a pen showing the problem, simplified. http://codepen.io/ghepting/pen/vBmLy
As you can see in the markup, I have tried including the "_" inside of the interpolated string as well as outside of it. Is there something I'm missing to work around this limitation of how Sass supports interpolation?
(Note: the OP's pen has disappeared. This is not the original code found in the pen, but a rough approximation of the problem)
$error-light: red;
$error-dark: darken(red, 10%);
$success-light: green;
$success-dark: darken(green, 10%);
$dialogs: error, success;
#each $d in $dialogs {
.#{$d} {
background: $#{$d}-light;
}
}

Answer 1

Interpolation doesn't work on mixins or variables at this point in time. You'll have to come up with a different way to achieve your goal.
As of Sass 3.3, you can use mappings for this purpose for variables:
$dialogs:
( error:
( light: red
, dark: darken(red, 10%)
)
, success:
( light: green
, dark: darken(green, 10%)
)
);
#each $name, $colors in $dialogs {
.#{$name} {
color: map-get($colors, dark);
}
}
And for functions:
#function green() {
#return lighten(green, 10%);
}
#function red() {
#return lighten(red, 10%);
}
#mixin my-bg($function-name) {
background: call($function-name);
}
.foo {
#include my-bg('red');
}

Answer 2

Alternative workaround (for a particular use case):
https://sass-lang.com/documentation/at-rules/mixin#passing-arbitrary-arguments
💡 Fun fact:
Because an argument list keeps track of both positional and keyword arguments, you use it to pass both at once to another mixin. That makes it super easy to define an alias for a mixin!
If you are interested in mixin interpolation because you have a group of mixins, like this:
//_mixins.scss
#mixin text-style-1($args...){ //sass here }
#mixin text-style-2($args...){ //sass here }
#mixin text-style-3($args...){ //sass here }
//_text.scss
.text-style-1 {
#include text-style-1;
}
.text-style-1-contrast {
#include text-style-1($contrast: true);
}
.text-style-2 {
#include text-style-2;
}
.text-style-2-contrast {
#include text-style-2($contrast: true);
}
We can take advantage of passing arbitrary arguments and use an alias for the group:
//_mixins.scss
#mixin text-style-1($args...){ //sass here }
#mixin text-style-2($args...){ //sass here }
#mixin text-style-3($args...){ //sass here }
#mixin text($mixin, $args...) {
#if $mixin == 'style-1' { #include text-style-1($args...); }
#else if $mixin == 'style-2' { #include text-style-2($args...); }
#else if $mixin == 'style-3' { #include text-style-3($args...); }
}
//_text.scss
$text-styles: 'style-1', 'style-2', 'style-3';
#each $style in $text-styles {
.text-#{$style} {
#include text($style);
}
.text-#{$style}-contrast {
#include text($style, $contrast: true);
}
}

Answer 3

Ran into this issue of trying to include an interpolated variable inside a mixin and was able to resolve it with placeholders:
%color-scheme-dark-bg-1 { background-color: #4e5163; }
%color-scheme-dark-color-1 { color: #4e5163 !important; }
%color-scheme-light-bg-1 { background-color: #c7c8ce; }
%color-scheme-dark-bg-2 { background-color: #fd6839; }
%color-scheme-dark-color-2 { color: #fd6839 !important; }
%color-scheme-light-bg-2 { background-color: #fecfc1; }
.card_color {
#mixin CardColorScheme($arg: 1) {
.borderPercent {
#extend %color-scheme-dark-bg-#{$arg};
}
.border {
#extend %color-scheme-light-bg-#{$arg};
}
ul li:before {
#extend %color-scheme-dark-color-#{$arg};
}
.percent {
#extend %color-scheme-dark-color-#{$arg};
}
.heading {
#extend %color-scheme-dark-color-#{$arg};
}
}
&--scheme {
&-1 {
#include CardColorScheme(1);
}
&-2 {
#include CardColorScheme(2);
}
}
}
Hat tip to: https://krasimirtsonev.com/blog/article/SASS-interpolation-in-a-name-of-variable-nest-variables-within-variables