Hello,
using only-in in a require statement can improve the memory footprint? It’s a good practice?
Matteo
My understanding: The granularity is modules.
By using require at all you pay the speed and space cost for requiring the entire module -- as well as all the modules it transitively requires, that aren't already required.
This can be significant, for example racket vs. just racket/base.
Clauses like only-in don't change this; they're not an optimization for space or speed (the entire module(s) will still be instantiated). Instead they're about visibility: You don't want to expose all the exported definitions, just some. You want to be explicit that you're importing the module to get what from it, exactly.
One example: If you have some local definition of foo, and require a module m just to use its exported bar, great, but someday m could decide to start exporting something called foo, too. Strictly speaking, exporting new things breaks backward compatibility. Clauses like only-in, prefix-in, rename-in are ways for importers to handle that, as well as potentially make the code and intent clearer.
4 Likes