Schwartzian Transform - Comparison To Other Languages

Comparison To Other Languages

Some other languages provide a convenient interface to the same optimization as the Schwartzian transform:

• In Python 2.4 and above, both the sorted function and the in-place list.sort method take a key= parameter that allows the user to provide a "key function" (like foo in the examples above). In Python 3 and above, use of the key function is the only way to specify a custom sort order (the previously-supported comparator argument was removed). Before Python 2.4, developers would use the lisp-originated Decorate-Sort-Undecorate (DSU) idiom, usually by wrapping the objects in a (sortkey, object) tuple.
• In Ruby 1.8.6 and above, the Enumerable abstract class (which includes Arrays) contains a sort_by method which allows you to specify the "key function" (like foo in the examples above) as a code block.
• In D 2 and above, the schwartzSort function is available. It might require less temporary data and be faster than the Perl idiom or the decorate-sort-undecorate idiom present in Python and Lisp. This is because sorting is done in-place and only minimal extra data (one array of transformed elements) is created.
• Racket's core sort function accepts a #:key keyword argument with a function that extracts a key, and an additional #:cache-keys? requests that the resulting values are cached during sorting. For example, a convenient way to shuffle a list is (sort l < #:key (λ (_) (random)) #:cache-keys? #t).