From: Martin DeMello <martindemello@...>
Date: 2006-07-07T22:26:33+09:00
Subject: Re: Float#==. Legacy?

On 7/6/06, Guillaume Marcais <guslist@free.fr> wrote:
> As far as my experience goes, using Float#== is always an error. Float
> should be compared within epsilon because of errors, etc. etc. But the
> question is: why keep Float#== if it is basically useless? Why not have
> Float#== be defined in the core by:
>
> class Float; def ==(o); ((o - self).abs < 0.0000001); end; end
>
> (Most likely with 0.0000001 be a parameter of the Float class so it can
> be changed at runtime.) Is the current implementation of Float#==
> legacy from C (and pretty much every other language I can think of)?
>
> It would make the behavior of Float more natural to humans and should
> not break much, given the uselessness of today's Float#==.

This is ugly, because Float#== is a two-argument method that you're
faking with one argument and one global constant. An array argument
might be a nice piece of syntactic sugar, though I'd still prefer to
overload =~ instead, e.g. a =~ [b, epsilon] with a =~ b defaulting to
Float::EPSILON.

Also, note that your method definition needs to be

def =~ (o); ((o - self)/o).abs <= EPSILON; end

you want relative, not absolute, error margins.

martin