Avoiding Naming Collisions with Namespaces

[noraj]

Bug Report

I'm sorry if it is not a bug, as the variable workaround works in ruby and not in crystal I thought this could be a bug.

Summary

Avoiding Naming Collisions with Namespaces can be solved by setting the built-in class to a variable before defining the custom module class in Ruby, but it doesn't work in Crystal (cf. https://flylib.com/books/en/2.44.1/avoiding_naming_collisions_with_namespaces.html).

Details

Crystal naming collision

test.cr

cat test.cr 
require "socket"

module Test1
  def self.test2(addr : String)
    Socket::IPAddress.new(addr, 8080)
  end

  class Socket
    # something else
  end
end

Test1.test2("127.0.0.1")

$ crystal run test.cr 
Showing last frame. Use --error-trace for full trace.

In test.cr:5:5

 5 | Socket::IPAddress.new(addr, 8080)
     ^----------------
Error: undefined constant Socket::IPAddress

Ruby naming collision

test.rb

require "socket"

module Test1
  def self.test2
    Socket::Option.bool(:INET, :SOCKET, :KEEPALIVE, true)
  end

  class Socket
    # something else
  end
end

Test1.test2

$ ruby test.rb
test.rb:5:in `test2': uninitialized constant Test1::Socket::Option (NameError)
        from test.rb:13:in `<main>'

Workaround naming collision in Ruby with variable

test.rb

require "socket"

module Test1
  RubySocket = Socket

  def self.test2
    RubySocket::Option.bool(:INET, :SOCKET, :KEEPALIVE, true)
  end

  class Socket
    # something else
  end
end

Test1.test2

ruby test.rb (no error)

(Trying to) Workaround naming collision in Crystal with variable

test.cr

require "socket"

module Test1
  CrystalSocket = Socket

  def self.test2(addr : String)
    CrystalSocket::IPAddress.new(addr, 8080)
  end

  class Socket
    # something else
  end
end

Test1.test2("127.0.0.1")

$ crystal run test.cr 
Showing last frame. Use --error-trace for full trace.

In test.cr:7:5

 7 | CrystalSocket::IPAddress.new(addr, 8080)
     ^-----------------------
Error: undefined constant CrystalSocket::IPAddress

Still encounter the same error.

Yes it is possible to rename the class from the custom module

Yes I know it is possible to rename the class in the module (like the code below) to avoid conflicts with the built-in class inside the module scope. But I would rather know how can I explicitly call the built-in Socket in a module scope while there is a class with the same name. Outside of Test1 scope there is no conflict with Socket and Test1::Socket.

require "socket"

module Test1
  def self.test2(addr : String)
    Socket::IPAddress.new(addr, 8080)
  end

  class SocketCustom
    # something else
  end
end

Test1.test2("127.0.0.1")

Env

$ crystal -v
Crystal 1.7.3 (2023-03-07)

LLVM: 14.0.6
Default target: x86_64-pc-linux-gnu

[Blacksmoke16]

But I would rather know how can I explicitly call the built-in Socket in a module scope while there is a class with the same name. Outside of Test1 scope there is no conflict with Socket and Test1::Socket.

You can just do ::Socket::IPAddress.new(addr, 8080). The :: prefix denotes it should use the top level type and not the local scope one. This feature also works for methods. E.g. ::raise "foo" if you had a locally defined #raise(message) method.

I don't actually think this is really documented anywhere, so if you would open an issue on https://github.com/crystal-lang/crystal-book, that would be 🙏. Going to close this one given it's already a thing.

[noraj]

I PRed the doc: crystal-lang/crystal-book#680

[straight-shoota]

The top-level scope prefix is actually documented in https://crystal-lang.org/reference/1.7/syntax_and_semantics/the_program.html#top-level-scope