From: Alder Green <alder.green@...>
Date: 2006-05-26T18:10:42+09:00
Subject: Re: Method '!='

On 5/26/06, Justin Collins <collinsj@seattleu.edu> wrote:
>
>
> Alder Green wrote:
> > On 5/26/06, Dave Burt <dave@burt.id.au> wrote:
> >> On 5/26/06, Alder Green wrote:
> >> > Trying to define a method != doesn't wfm, even with define_method:
> >> >
> >> > irb(main):013:0> class Object; define_method(:!=) {|arg| self !=
> >> arg }; end
> >> > class Object; define_method(:!=) {|arg| self != arg }; end
> >> >
> >> > SyntaxError: compile error
> >> > (irb):13: parse error, unexpected tNEQ, expecting tSTRING_CONTENT or
> >> > tSTRING_DBEG or tSTRING_DVAR or tSTRING_END
> >> > class Object; define_method(:!=) {|arg| self != arg }; end
> >> >                                ^
> >>
> >> No, just that symbol syntax. :!= is not a valid symbol. "!=" will work
> >> just fine, though.
> >>
> >> irb(main):001:0> class << self
> >> irb(main):002:1> define_method("!=") {}
> >> irb(main):003:1> end
> >> => #<Proc:0x00000000@(irb):3>
> >>
> >> Cheers,
> >> Dave
> >
> > Yup, good tip. However, the relations between the operator syntax and
> > the method calls reveals itself to be more mysterious than I thought:
> >
> > class Foo
> >  define_method('!=') { 'Foo#!= was called' }
> >  define_method('==') { 'Foo#== was called' }
> > end
> >
> > irb(main):003:0> foo = Foo.new
> > #<Foo:0x2c88e28>
> >
> > irb(main):004:0> foo != 1
> > false   # looks like 'foo != arg' isn't simply syntactic sugar for
> > !foo.==(arg)
> >
>
> Actually, it still is:
>
> foo.==(1) returns the string 'Foo#== was called' which is true. Then it
> is negated: false.
>
> Try changing it to:
>
> class Foo
>  define_method('!=') { puts 'Foo#!= was called' }
>  define_method('==') { puts 'Foo#== was called' }
> end
>
> And you will see it call '=='.
>
> -Justin
>

Do'h!  You are correct, of course.

-- 
-Alder