What is the meaning of '{**}' in Pathname#join

Question

In my Rails project in application.rb file there is a line, which is written by some previous developer who was working on the project.

config.autoload_paths += Dir[Rails.root.join('app', 'classes', '{**}')]

I know that autoload_paths is used by rails to load all required files. I am not able to figure out the meaning of {**}. Does this means all files and sub directories of classes directory will be loaded? Is there any documentation which I can refer for this.

I have done some debugging.

2.2.5 :008 > Rails.root.join('app', 'classes', '{**}')
 => #<Pathname:/home/tk/src/project-name/app/classes/{**}>

This is actually a Pathname object. But I have not found any reference about {**} here.

Does any one have any idea what is {**}? Is there any documentation for this?

score 4 · Accepted Answer · answered Nov 17 '16 at 07:42

4

Pathname just builds a path, it does not care about parts.

** is a parameter to Dir#[] which is eventually an alias to Dir#glob.

** means “match directories recursively.”

answered Nov 17 '16 at 07:42

Aleksei Matiushkin

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Also, `{..}` is used for grouping and alternation in globs (e.g. `{foo,ba{r,z},q*}` should match `foo`, `bar`, `baz`, `quux` but not `charlie`). `{**}` should be identical to `**`. – Amadan Nov 17 '16 at 07:50
@Amadan yes, indeed, `{**}` **is** identical to `**`. – Aleksei Matiushkin Nov 17 '16 at 07:52

score 2 · Answer 2 · answered Nov 17 '16 at 07:57

This is a feature of Dir.glob, though I'm not sure why this is used the way it is here. {...} is a grouping mechanism, but there's only one element in it, **, which is a recursive matcher.

You should be fine with:

Dir[Rails.root.join('app', 'classes', '**')]

Or if you like something more conscise:

Dir[Rails.root.join(*%w[ app classes ** ]]

What is the meaning of '{**}' in Pathname#join

2 Answers2