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Optimize Dir.glob #8081

merged 1 commit into from Aug 28, 2019


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commented Aug 14, 2019

This PR optimized Dir.glob by avoiding unnecessary calls to for each directory entry because readdir already gives us that information.

This is similar to how Python does it since some time ago and I can imagine Ruby does that too, probably other languages as well.

I just wanted to optimize this so the public API is still the same. I just exposed internally the information of whether a dir entry is a directory or not just for this purpose.

In the future we can consider whether it makes sense to expose this information in a public API but right now I'd like to avoid huge breaking changes, or having to think about new APIs. I think the change here is pretty straight-forward and small that it's not a big deal to introduce this optimization.

I wrote this benchmark:

require "benchmark"

Benchmark.ips do |x|"Dir.glob") do
    Dir.glob("*/*.cr") do


before: 1.73k (578.82µs) (± 2.60%)  67.3kB/op
after:  2.46k (407.11µs) (± 0.82%)  67.8kB/op
RX14 approved these changes Aug 28, 2019
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This should really be exposed in the public API. This is really quite an especially ugly optimization.

Is this optimization worth rushing and not designing the API properly? I'm not sure. But I'm fine to approve it if an issue is created for adding the API to Dir.

@asterite asterite added this to the 0.31.0 milestone Aug 28, 2019
@asterite asterite merged commit 36a7557 into crystal-lang:master Aug 28, 2019
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