Ruby load does not see static methods in the class

Question

I am experimenting with ruby (2.4.1p111) and with the load method and it does have some strange behavior:

I have two files:

mytest.rb:

class MyClass

  def self.greet(param)
   puts "Got called: #{param}"
  end

  greet 'Called locally'

  load "./testld.rb"
end

and the loaded file:

testld.rb:

greet 'Called by load'

I understood from documentation that the loaded code from testld.rb and the method call right in the MyClass should behave the same. Instead, I am getting:

-bash-4.2$ ruby mytest.rb
Got called: Called locally
/Blacksmith/RB/testld.rb:1:in `<top (required)>': undefined method `greet' 
for main:Object (NoMethodError)
    from mytest.rb:9:in `load'
    from mytest.rb:9:in `<class:MyClass>'
    from mytest.rb:1:in `<main>'

Any idea what I do wrong?

Could you point to the documentation that left you with such understanding? That is not how it works. If it was enclosed in MyClass in testld.rb, it will be called as if it was. If it was not, it will not, no matter where you load it. — ndnenkov
– ndnenkov, Commented Aug 9, 2017 at 14:23
ruby-doc.org/core-2.4.1/Kernel.html#method-i-load I wrongly assumed the loaded code is executed in the context of the MyClass. MyClass.greet does the work as @MatayoshiMariano has pointed out. — Pavel
– Pavel, Commented Aug 9, 2017 at 14:46
@Pavel "I wrongly assumed the loaded code is executed in the context of the MyClass." That is not what MatayoshiMariano pointed out. That answer misses the point. — sawa
– sawa, Commented Aug 9, 2017 at 14:46
@Pavel you want something like eval File.read('testld.rb') but load doesn't work that way. — Stefan
– Stefan, Commented Aug 9, 2017 at 14:59
@Pavel, I couldn't see how you got this interpretation. I agree that Ruby's namespacing is one of it's weaker points, but it's not as terrible as for load to perform a copy-paste. xd — ndnenkov
– ndnenkov, Commented Aug 9, 2017 at 14:59

MatayoshiMariano · Accepted Answer · 2017-08-09 14:27:03Z

2

You need to call MyClass.greet in testld.rb, that is because greet is a class method defined in the class MyClass.

Here is documentation for class methods.

answered Aug 9, 2017 at 14:27

MatayoshiMariano

2,14619 silver badges24 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

sawa Over a year ago

@Pavel The fact that it works is coincidence. This answer is irrelevant to your actual question.

sawa Over a year ago

Is anything mentioned in this answer specific to Ruby 2.4, whose tag MatayoshiMariano added to the suggested edit?

MatayoshiMariano Over a year ago

@sawa I do not think that is a coincidince, but my answer may be incomplete, it's missing what load does. I added the ruby-2.4 tag because @Pavel says that he is using ruby 2.4.1p111

sawa · Accepted Answer · 2017-08-09 14:43:16Z

1

Wherever you load a file, the loaded file is always evaluated within the main environment. The value of self in the main environment of testld.rb is the main environment of the entire script. Hence, your

greet 'Called by load'

is not equivalent to

MyClass.greet 'Called by load'

as you expected.

answered Aug 9, 2017 at 14:43

sawa

169k51 gold badges287 silver badges398 bronze badges

4 Comments

Pavel Over a year ago

What I really wanted to achieve is to have the static method called, the MyClass.greet. I thought that the load works kind of like a C preprocessor, placing the file content into the MyClass and then execute, which was wrong.

sawa Over a year ago

You do have defined MyClass.greet. That part, you did correctly. What you did wrong is the way you called it. And here is the explanation to it.

tadman Over a year ago

@Pavel Don't think of Ruby as a fancy C. It's Smalltalk in origin which has a different approach to solving problems like this. If you created a module and include it in your class you'll be able to hook in through the included method and everything should work seamlessly.

Jörg W Mittag Over a year ago

@Pavel: load, require, and require_relative simply run the file. That's all they do.

Collectives™ on Stack Overflow

Ruby load does not see static methods in the class

2 Answers 2

3 Comments

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related