Sass @include or @extend with generated selectors & override-able rules

_include-or-extend-defaults.scss

// ---------------------------------------

/*

http://codepen.io/morewry/pen/meBtj

Use case for defaults:
providing interface points to override framework defaults with more flexibility and granularity than variables can reasonably provide, ie customize normalizations without editing the stylesheet directly (@content in reverse)

Use case for swapping extend or include:
Optimize generated css, debug source order problems

This provides a workaround to lack of dynamic mixin names and includes to some degree.

*/

$gr-default-method: extend !default;
$gr-default-merge: false !default;
$gr-default-debug: false !default;

// ---------------------------------------

@mixin map-as-css ($map) {
	@each $p, $v in $map {
		#{$p}: #{$v};
	} // each
} // @mixin map-as-css

// ---------------------------------------

@function set-rules ( $name, $rules, $merge ) {
	$nooverrides: (not $rules or (type-of($rules) != map) or length($rules) < 1);
	$nodefaults: (not variable-exists(default-rules) or (type-of($default-rules) != map) or length(map-get($default-rules, $name)) < 1);
	// Get rules to generate
	@if $nodefaults and $nooverrides {  
		@warn "@mixin get-rules didn't find any rules for #{$name}";
	}
	@if not $nodefaults and $nooverrides {
		$rules: map-get($default-rules, $name);
	}
	@if $merge and not $nooverrides {
		$rules: map-merge(map-get($default-rules, $name), $rules);
	} // merge overrides
	@if not $nooverrides {
		$default-rules: map-merge($default-rules, ($name: $rules)) !global;
	}
	@return $rules;
} // @function set-rules

// ---------------------------------------

@mixin get-rules ( $name, $method: $gr-default-method, $rules: false, $merge: $gr-default-merge, $debug: $gr-default-debug  ) {
	$rules: set-rules($name, $rules, $merge);
	// init rules and placeholder
	@if $method == init { 
		@if length($rules) {
			%#{$name} {
				@include map-as-css($rules);
			} // placeholder
			@if $debug {
				.#{$name} {
					@extend %#{$name};
				} // class
			} // debug
		} // use overrides
	} // init
	// @extend or @include rules
	@else {
	 @if $method == extend {
			@extend %#{$name} !optional;
		} // extend
		@else {
			@include map-as-css($rules);
		} // include
	} // use
} // @mixin get-rules

// ---------------------------------------

$default-rules: (
	test: (
		margin: 1em,
		padding: 0.25em,
		color: #fff,
		background-color: #f00,
		font-weight: bold
	), // test
	another: (
		border-radius: 25%
	) // another
); // $default-rules

/*
Usage:

// ---------------------------------------

$newprops: (
	color: #0f0,
	background-color: #00f
);

// ---------------------------------------

// init (required for @extend, but not for @include)
@include get-rules($name: "test", $method: init, $rules: $newprops, $merge: true, $debug: true);

// ---------------------------------------

// test @extend
.test-extend { @include get-rules("test", extend); }

// test @include
.test-include { @include get-rules("test", include); }

// test vanilla @extend
.test-vanilla-extend { @extend %test !optional; }

// ---------------------------------------

*/