Ruby: require vs include/extend: Using a module inside another, but not exposing to users
ruby inheritance vs include
rails include module
ruby include class
I was having trouble understanding an error while unit testing my module, which is a mixin.
Suppose the mixin to be tested is module A:
require 'path/b' module A def methodA() puts methodB.attr1 end end
And it depends on another mixin B which was defined in a file at path/b.rb
module B def methodB return someObject #that has property 'attr1' end end
Now, we have a class to unit test module A
require 'path/moduleA' class TestA include Path::moduleA end describe 'test moduleA.methodA' it 'does something' testObject = TestA.new testObject.methodA() expect(....) end end
I get following error on running the rspec test
NameError: undefined local variable or method `methodB' for #<TestA:0x00007f77a03db9a8>
I am able to resolve it by one of following ways:
- including module B in module A
- including module B in class TestA
I am not clear why include is required to get access to methodB in module A and class TestA when 'require' was already added in module A.
My intention is to use methods of module B in module A, but not let users of module A access module B methods automatically.
resolution 1 above gives users of A, access to B's methods
resolution 2 forces users of A (user -> the unit test class in this example) to include A's dependency B directly, even though user is only interested in accessing A's methods.
Hence, both resolutions don't achieve what I want. Is there a way to achieve it?
I'm new to Ruby so may be it doesn't support this. I'm from Java background where I would model A and B as two classes, make an instance of B as field of A, then expose A's own public methods to users of A. But since they are mixins, I need to use modules in ruby.
Just to be very explicit:
prepend have absolutely nothing whatsoever to do with each other.
The former three simply run a Ruby file. That's it. That is all they do. They differ in how and where they search for the file, but after they found the file, they don't do anything else than just execute it.
The latter three add a module to the ancestor chain.
include essentially makes the module the superclass,
extend is really the same as
singleton_class.include (i.e. makes the module the superclass of the singleton class), and
prepend inserts the module at the beginning of the ancestor's chain, i.e. actually before the class that it is prepended to.
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require just tells ruby to read / load the code inside the ruby file. In this case it will just define the module. However in order for code inside a module to be included inside another module or class, you must
include it inside the module or class. So you should just as you mentioned do:
require 'path/b' module A include B def methodA() puts methodB.attr1 end end
You should not need to change your test with this since module A already includes module B. However this is not a very good OOP design pattern here. But hopefully you understand why now.
Ruby Methods: differences between load, require, include and , Ruby Methods differences: load vs require vs include vs extend in Ruby. The load method simply reads and parses another files into your code then we can use the load 'test_module.rb' just before the class definition in won't be applied - Ruby will use the file from memory, not from the file system. You can access variables, functions, and mixins from another module by writing <namespace>.<variable>, <namespace>.<function>(), or @include <namespace>.<mixin>(). By default, the namespace is just the last component of the module’s URL. Members (variables, functions, and mixins) loaded with @use are only visible in the stylesheet that loads
After more googling, I found the answer to my 2nd question using suggestion from: https://makandracards.com/makandra/977-calling-selected-methods-of-a-module-from-another-module
so basically i did:
require 'path/b' module A module B_RequiredMethods include Path::B module_function :methodB end def methodA puts B_RequiredMethods.methodB.attr1 end end
In my case, B_RequiredMethods could be named properly to represent the method of B which would be exposed by it. Ideally, I would make those methods class level methods of B, but it is managed by some other team.
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Logic Programming: 25th International Conference, ICLP 2009, , Here we use the Thea library, which exposes OWL axioms directly as Prolog predicates. Thea is being extended to handle OWL2. One possible solution would be to use dot to perform the layout, and then use this to guide placement within For prolog applications, this has the advantage that the end user does not While @extend is allowed within @media and other CSS at-rules, it’s not allowed to extend selectors that appear outside its at-rule. This is because the extending selector only applies within the given media context, and there’s no way to make sure that restriction is preserved in the generated selector without duplicating the entire style
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- I think my question is similar to stackoverflow.com/questions/322470/…
- If i include module B in module A, all of the methods of B become methods of A due to inheritance. However, i want to use methods of B in A without exposing them to users of A. Is it acheivable? Reason for this is that module A is a different class from module B and doesn't make sense to inherit it. One way is to let users of A include B but then they become aware of what modules A depends on, thats not right either.
- "If i include module B in module A, all of the methods of B become methods of A due to inheritance." – No, they don't. The methods of
Bare methods of
B, period. If you include module
A, then the only thing that happens is that Ruby records the fact that you did this. Then, later, when you include
Binto some class
C, Ruby will make
Bthe new superclass of
Athe superclass of
B, and the old superclass of
Cthe superclass of
A. At no point whatsoever does a method of one module or class become a method of another module or class.