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comp.lang.ruby

Kernel.=== in case statements, even though I never called it

Jesse Silliman

9/5/2006 12:18:00 AM

I was profiling a script I wrote, and the method with the greatest
amount of time used was Kernel.=== . I was surprised, not only since I
didn't use this method in my code, but my code had nothing involving
modules. When I changed a case statement that was inside my loop to an
if and many elsifs, I saved about 2 seconds on profiling, and the call
was gone. Is there a reason such a slow call is used in case statements?

--
Posted via http://www.ruby-....
3 Answers

Tomasz Wegrzanowski

9/5/2006 12:23:00 AM

0

On 9/5/06, Jesse Silliman <wierdbro@gmail.com> wrote:
> I was profiling a script I wrote, and the method with the greatest
> amount of time used was Kernel.=== . I was surprised, not only since I
> didn't use this method in my code, but my code had nothing involving
> modules. When I changed a case statement that was inside my loop to an
> if and many elsifs, I saved about 2 seconds on profiling, and the call
> was gone. Is there a reason such a slow call is used in case statements?

case uses === (pattern match) not ==.

It is very useful:

case str
when /foo/
...
end

case num
when 3..5
...
end


--
Tomasz Wegrzanowski [ http://t-a-w.blo... ]

Jesse Silliman

9/5/2006 12:28:00 AM

0

Tomasz Wegrzanowski wrote:
>
> case uses === (pattern match) not ==.
>
> It is very useful:
>
> case str
> when /foo/
> ...
> end
>
> case num
> when 3..5
> ...
> end

Oh, I'm quite aware of that. Oh... its calling the objects inherited
Kernel.===, not calling Kernel::===. Ok, well, in that case, a good
question would be "Why is it so much slower in simple cases than == is,
even though for string they do the exact same thing?"

--
Posted via http://www.ruby-....

Tomasz Wegrzanowski

9/5/2006 1:20:00 AM

0

On 9/5/06, Jesse Silliman <wierdbro@gmail.com> wrote:
> Oh, I'm quite aware of that. Oh... its calling the objects inherited
> Kernel.===, not calling Kernel::===. Ok, well, in that case, a good
> question would be "Why is it so much slower in simple cases than == is,
> even though for string they do the exact same thing?"

Kernel#=== calls == method, not aliases it. So you have 2 method calls,
and two dynamic dispatches instead of one: Kernel#===, then String#==.

You can test this by alias_method'ing === to == in String class ;-)

Relevant code:
VALUE
rb_equal(VALUE obj1, VALUE obj2)
{
VALUE result;

if (obj1 == obj2) return Qtrue;
result = rb_funcall(obj1, id_eq, 1, obj2);
if (RTEST(result)) return Qtrue;
return Qfalse;
}


--
Tomasz Wegrzanowski [ http://t-a-w.blo... ]