From: Chad Perrin <code@...>
Date: 2011-07-04T01:33:58+09:00
Subject: Re: symbol vs string for hash keys

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On Mon, Jul 04, 2011 at 12:28:03AM +0900, Intransition wrote:
> What are the important factors to consider when deciding whether to
> use symbols or strings for hash keys?
>=20
> I ask b/c I noticed that fileutils.rb uses strings[1], though the keys
> represent method names. Seems to me that symbols would be more
> appropriate.
>=20
> Even so it would be good to know the general criteria to consider.
>=20
> [1]https://github.com/ruby/ruby/blob/trunk/lib/fileutils.rb
> (OPT_TABLE)

Strings are mutable; symbols are not.

There is only one instance of any given literal symbol; there can be many
instances of a given literal string.

Basically, if it is more important to be able to operate on the names of
your hash keys, strings are appropriate; if performance is more
important, or you are sure no such operation on the names will be
necessary, symbols are appropriate.

It also makes sense to consider the fact that if you're selecting hash
keys based on some kind of input, strings are easier -- because inputs
tend to be strings rather than symbols, and would thus need to be
translated into symbols if you use symbols as your hash keys.

That's the ugly, hand-wavy, implementation-aware answer, I guess.  The
more conceptual answer is that symbols are identities and strings are
data.

I suspect strings are used in the example you provided because it is
expected that when dealing with OPT_TABLE one might operate on a string
in some manner before using it as a hash key.  I'm really not sure,
though.

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

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