How to get all class names in a namespace in Ruby?

Question

I have a module Foo, that it is the namespace for many classes like Foo::Bar, Foo::Baz and so on.

Is there an way to return all class names namespaced by Foo?

score 76 · Accepted Answer · edited Sep 24 '13 at 15:37

76

Foo.constants

returns all constants in Foo. This includes, but is not limited to, classnames. If you want only class names, you can use

Foo.constants.select {|c| Foo.const_get(c).is_a? Class}

If you want class and module names, you can use is_a? Module instead of is_a? Class.

edited Sep 24 '13 at 15:37

Matt Briggs

answered Sep 09 '10 at 12:02

sepp2k

1

This is a great answer. You sort of forget sometimes that constants in ruby are anything that _starts_ with a capital, so class names are constant instances of type class. +1 – Matt Briggs Sep 09 '10 at 12:32
5

@jcaudle Ruby does *not* lazy load classes. You're thinking of Rails. – sepp2k Sep 20 '13 at 15:13
6

Make sure you load all the classes before: `Dir["app/models/foo/*.rb"].each {|file| load file}` – espinchi Dec 15 '13 at 16:04
1

@espinchi When giving Rails-specific advice, it is best to say so. Otherwise it might confuse people. – sepp2k Dec 15 '13 at 17:06
2

This only works for classes that have been previously loaded. – jaydel Aug 12 '19 at 13:49
This is NOT the correct answer, as it depends on the autoloader and loading strategies. When your class is never referenced/ needed, thus the file never looked-up via the autoloader, the class will not be listed with the constants. The reference of constants will NOT contain all the constants, because of this issue. – Dennis Dec 15 '21 at 10:09

score 42 · Answer 2 · answered Sep 09 '10 at 21:29

42

If, instead of the names of the constants, you want the classes themselves, you could do it like this:

Foo.constants.map(&Foo.method(:const_get)).grep(Class)

answered Sep 09 '10 at 21:29

Jörg W Mittag

5

I *love* point-free programming. Is my Haskell showing through? – Jörg W Mittag Sep 09 '10 at 21:29
1

I'll buy you a beer for this answer! – Andrew Ashbacher Jul 17 '11 at 01:44
1

This answer was best but ensuring it was defined prevents crashes from things like Module::MODULES `Module.constants.select(&Module.method(:const_defined?)).map(&Module.method(:const_get)).grep(Class)` – Aeramor Jul 06 '16 at 14:11

score 16 · Answer 3 · answered Jul 23 '13 at 15:00

16

In short no. However, you can show all classes that have been loaded. So first you have to load all classfiles in the namespace:

Dir["#{File.dirname(__FILE__)}/lib/foo/*.rb"].each {|file| load file}

then you can use a method like Jörg W Mittag's to list the classes

Foo.constants.map(&Foo.method(:const_get)).grep(Class)

answered Jul 23 '13 at 15:00

Silverdev

2

This approach is problematic if you are inspecting modules at runtime – Gerard Simpson May 03 '19 at 00:31
This is the ONLY correct answers, as it omits the workings of the autoloader! – Dennis Dec 15 '21 at 10:09

score 14 · Answer 4 · answered Jan 05 '12 at 18:47

14

This will only return the loaded constants under the given namespace because ruby uses a lazy load approach. So, if you type

Foo.constants.select {|c| Foo.const_get(c).is_a? Class}

you will get

[]

but after typing:

Foo::Bar

you will get

[:Bar]

answered Jan 05 '12 at 18:47

Pikachu

Make sure you load all the classes before: Dir["app/models/foo/*.rb"].each {|file| load file} – bsvin33t May 22 '19 at 12:21

score 1 · Answer 5 · answered Aug 12 '21 at 03:22

This alternative solution will load and show all classes under Foo:: including "nested" classes, e.g. Foo::Bar::Bar.

Dir["#{File.dirname(__FILE__)}/lib/foo/**/*.rb"].each { |file| load file }
ObjectSpace.each_object(Class).select { |c| c.to_s.start_with? "Foo::" }

Note: **/*.rb recursively globs.

If you want to include the Foo class itself, you could change your select to e.g. { |c| c.to_s =~ /^Foo\b/ }

5 Answers5