From: John Carter <john.carter@...>
Date: 2006-04-03T06:03:48+09:00
Subject: Re: Typed Parameters

On Sun, 2 Apr 2006, Robert Dober wrote:

> Dear group
>
> there was a recent thread about "Boolean" and it braught me to my favorit
> thing I would love to have in Ruby2.
>
> *typed parameters*
>
> My code is completely filled with things like this:
>
> def never_saw_a_better_method( clever, smart, stupid )
>            assert_type clever, String
>           assert_type  smart, Hash
>          assert_type  stuoid, Boolean
> ....
> def cool( clever : String, smart : Hash, stupid : Boolean )
>
> and of course
> def x(y)  would be equivalent to def(x : Object )

Howabout what I do..


def never_saw_a_better_method( clever, smart, stupid )
   clever.static_type_check String
   smart.quacks_like :each_pair
   stupid.poymorphic_type_check SomeBaseClass
end


# Abstract base class for all the type check exceptions
class TypeCheckException  < Exception
end

# This exception is thrown in event of a method being invoked with an
# object of the wrong duck type.
class DuckTypingException < TypeCheckException
end

# This exception is thrown in event of a method being invoked with a
# parameter of of the wrong static type.
class StaticTypeException < TypeCheckException
end

# This exception is thrown in event of a method being invoked with a
# parameter of of the wrong polymorphic type.
class PolymorphicTypeException < TypeCheckException
end


class Object

   # Raise a DuckTypingException unless the object responds to all symbol.
   def quacks_like( *symbols)
     symbols.each do |symbol|
       raise DuckTypingException, "Duck typing error, expected this object to respond to :#{symbol}, but found class #{self.class}\n\t\t#{symbol.inspect}" unless
         respond_to? symbol
     end
   end

   def static_type_check( klass)
     raise StaticTypeException, "Static type check error, expected object to be exactly class '#{klass}', found '#{self.class}'\n\t\t#{self.inspect}" unless
       self.class == klass
   end

   def polymorphic_type_check( klass)
     raise PolymorphicTypeException, "Polymorphic type check error, expected object to be a kind of '#{klass}', found '#{self.class}'\n\t\t#{self.inspect}" unless
       self.kind_of? klass
   end

end


if $0 == __FILE__ then
   require 'test/unit'

   class TC_Utilities < Test::Unit::TestCase

     def test_utilities
       assert_raise( DuckTypingException) { nil.quacks_like( :call)}
       assert_raise( DuckTypingException) { 1.quacks_like( :+, :call)}
       1.quacks_like( :+, :-, :*)

       assert_raise( StaticTypeException) { nil.static_type_check( String)}

       assert_raise( PolymorphicTypeException) {"foo".polymorphic_type_check( Array)}

       begin
         2.static_type_check( String)
       rescue TypeCheckException => details
         puts details
       end
       begin
         2.polymorphic_type_check( String)
       rescue TypeCheckException => details
         puts details
       end
     end

   end


end



John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

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From this principle, all of life and physics may be deduced.