From: Chad Perrin <code@...>
Date: 2011-08-10T04:20:55+09:00
Subject: Re: *WHY* does this not work?

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On Wed, Aug 10, 2011 at 03:52:59AM +0900, serialhex wrote:
> ok, so code:
>=20
> str =3D 'foo'
> =3D> "foo"
> str.each_char do |c|
>   c =3D 'x'
> end
> =3D> "foo"

Try this:

    str.gsub!(/\w/, 'x')

>=20
> WHY does str =3D=3D 'foo' still?? i would expect it to be 'xxx'!

The common way to handle things in Ruby is to *not* change the receiver
of a message.  To do otherwise is surprising.


>=20
> ... i CAN'T do things like that for a string because it dsn't seem to do
> that, but for an array i'd have to:
>=20
> ary =3D ['f', 'o', 'o']
> =3D> ["f", "o", "o"]
> ary.each_index do |i|
>   ary[i] =3D 'x'
> end
> =3D> ["x", "x", "x"]

=2E . . or use a map:

    ary.map! {|element| element.sub /\w/, 'x' }


>=20
> GAH!!! least surprise??  least surprise my FOOT!!!  even if there was a
> *.each! method to do that i would be fine, *that* would be ok, none of th=
is
> 'get the index and then do what you need to do and *THEN* set the stupid
> block variable.... GRRRRRR!!!!

You're operating on c, not on str.  It would be more surprising if when
operating on c it changed str, in my opinion.

The each method is an iterator -- not an editor.  If you want to map an
operation onto an array, you should use the map method.  If you want to
do substitutions on characters in a string, use a substitution method.
What could be less surprising than using the right tool for the job?

I think you're surprised because you expect one tool to do *everything*.
I would be pretty surprised if someone could make such a tool that wasn't
bad at everything it did.

--=20
Chad Perrin [ original content licensed OWL: http://owl.apotheon.org ]

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