From: Tim Pease <tim.pease@...>
Date: 2006-07-07T01:55:24+09:00
Subject: Re: Float#==. Legacy?

If you are using Test::Unit, the assert_in_delta method should be used
for comparing floats.

I prefer the idea of an epsilon_eq? method for Float that takes
another float and a small epsilon. The epsilon would default to
Float::EPSILON which ruby alread defines.

Blessings,
TwP

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#==.
>
> As an example, some unit tests crashed today with this message:
>
>    1) Failure:
> test_read_coords(TestScaffoldReorder)
> [./test/test_scaffold_reorder.rb:50]:
> <{"9876"=>{"8153"=>[19.1, [63.7, 580.0]], "8154"=>[15.0, [1612.5]]}}>
> expected but was
> <{"9876"=>{"8153"=>[19.1, [63.7, 580.0]], "8154"=>[15.0, [1612.5]]}}>.
>
>
> It looks stupid, doesn't it? It failed because the computed float where
> not exactly equal to the constant entered in the testing code, but they
> display the same. I could drill down the hashes and compare with
> assert_within_epsilon (or whatever it is), but it makes the code much
> uglier and more complicated than a simple assert_equal. Or wrap the
> structure in a class and have a proper equality operator. Or...
> But all this seems too complicated for the quick program at hand. And
> redefining Float#== as shown above made the test pass with much less
> pain.
>
> So any good reason to keep Float#== the way it is? Or is there any real
> danger of breaking existing libraries if I redefine Float#== this way?
>
> Guillaume.
>
>
>