Memoization in Sass

generalized_memoizer.scss

// This approach lets you generically memoize any function by changing the call site:

@function something-slow-to-compute($arg-1, $arg-2) {
  @return ... slow calculation ... ;
}

$cached-values: ();
@function cached($function-name, $args...) {
  $cached-value: map-get($cached-values, ($function-name, $args));
  @if $cached-value {
    @return $cached-value;
  } @else {
    $result: call($function-name, $args...);
    $cached-values: map-merge($cached-values, (($function-name, $args): $result)) !global;
    @return $result;
  }
}

.output {
  slow-call: cached(something-slow-to-compute, 100, 500);
  fast-call: cached(something-slow-to-compute, 100, 500); // the second call is fast
}

one_off_memoization.scss

// This approach lets you memoize the results for all callers of this function.
$slow-computation-results: ();
@function something-slow-to-compute($arg-1, $arg-2) {
  $cached-value: map-get($slow-computation-results, ($arg-1, $arg-2));
  @if $cached-value {
    @return $cached-value;
  } @else {
    $result: ... slow calculation ... ;
    $slow-computation-results: map-merge($slow-computation-results, (($arg-1, $arg-2): $result)) !global;
    @return $result;
  }
}

.output {
  slow-call: something-slow-to-compute(100, 500);
  fast-call: something-slow-to-compute(100, 500); // the second call is fast
}