From: Justin Collins <collinsj@...>
Date: 2006-05-26T17:31:34+09:00
Subject: Re: Method '!='



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