How how access a local variable from another module

Help & Support
1

For example:

# src/a.cr
require "crsfml"

module A
  window = SF::RenderWindow.new(SF::VideoMode.new(1080, 720), "My Window", SF::Style::Close)
  # ...

# src/b.cr
require "crsfml"
require "./a"
module B
  A.window.framerate_limit = 60
  # ...

I’m new to Crystal, I think what I need is something like static variable in Java

2

Local variables at the top level of the module cannot be accessed outside that top level, including methods under the module.
You can instead make it a class variable or a constant, and make a method that returns the value of it.

module A
  extend self
  @@test = "A"
  
  def test
    @@test
  end
end
 
p A.test # => "A"

By adding extend self, every method under the module will essentially behave like def self.method_name, making it a static method that can be accessed outside that module.
https://crystal-lang.org/reference/1.5/syntax_and_semantics/modules.html#extend-self

class_getter is a shorthand macro to define a class variable and a getter method that returns the value, as well as class_property for both getter and setter, and class_setter for setter only.
https://crystal-lang.org/api/1.5.0/Object.html#class_getter(*names,&block)-macro

module A
  class_getter test = "A"
  # is the same as writing:
  # @@test = "A"
  # def self.test
  #   @@test
  # end
end
 
p A.test # => "A"
1 Like
3

Thanks, it truly makes sense!

But now there is another problem:

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Obviously, I have defined the lowp_mode boolean variable.
And before the class_getter macro was added, this problem didn’t exist.

4

I think that’s because class variables are always initialized before local variables.
If lowp_mode is not changing, you can change that to a constant. Otherwise, you might have to make that a class variable as well, but at that point, I think using module as a namespace is not suitable anymore.