Platform indepedent standard library for Crystal

lib_c.cr

lib LibC
  # Common bindings go here
  fun chdir(...)
  fun printf(...)
  fun wprintf(...)
  fun atoi(...)
  fun watoic(...)
end

ifdef windows
  require "./windows_c_wrapper"
elsdef linux
  require "./linux_c_wrapper"
end

linux_c_wrapper.cr

lib LibC
 # Platform specific bindings that might not exist on other platforms or
 # are incompatible

 fun linux_only(...)
 fun different_signature(...)
end

module CWrapper
  # Boilerplate could be reduced by macro usage, for example a macro method_missing

  def self.stat(path)
    LibC.stat(path)
  end

  def self.chdir(dir)
    LibC.chdir(dir)
  end

  def self.atoi(string)
    LibC.atoi(string)
  end

  def self.printf(format, args)
    LibC.printf(format, args)
  end
end

stdlib.cr

require "./lib_c"


class File
  def self.stat(path)
    CWrapper.stat(path)
  end
end

class Dir
  def self.chdir(dir)
    CWrapper.chdir(dir)
  end
end

class String
  def to_i
    Cwrapper.atoi(self)
  end
end


module Kernel
  def printf(format, args)
    CWrapper.printf(format, args)
  end
end

windows_c_wrapper.cr

lib LibC
 # Platform specific bindings that might not exist on other platforms or
 # are incompatible

 fun windows_only(...)
 fun different_signature(...)
end

module CWrapper
  # Boilerplate could be reduced by macro usage, for example a macro method_missing

  def self.stat(path)
    LibC.stat(path.to_utf16)
  end

  def self.chdir(dir)
    LibC.chdir(dir.to_utf16)
  end

  def self.atoi(string)
    LibC.watoi(string.to_utf16)
  end

  def self.printf(format, args)
    LibC.wprintf(format.to_utf16, args)
  end
end

An application that needs to care about different semantics between two functions, like atoi and watoi on Windows, is already by the fact that it needs to differentiate these, platform dependent. It has two choices:

1. It can regain platform independence by adding a new functionality to the standard library that has a common interface and behaviour on all platforms. The platform specific details of this implementation would be implemented in the respective wrapper modules. Due to Crystals open class model, this is trivial, however this scheme can also easily be replicated in the application itself.
2. It can stay platform dependent by bypassing the wrappers and calling the bindings directly in the application code, LibC.atoi instead of String#to_i or CWrapper.atoi.