From: Arlen Cuss <celtic@...>
Date: 2008-04-30T09:23:10+09:00
Subject: Re: Array#first is not Array#[0]

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Hi,

On Wed, Apr 30, 2008 at 4:50 AM, Brian Adkins <lojicdotcom@gmail.com> wrote:

> "David A. Black" <dblack@rubypal.com> writes:
> > The real question is: why should it? They're completely separate
> > methods.
>
> I can't think of a good reason to ever have: Array#first != Array#[](0)
>
>
They're still separate methods. The point is, internally, Ruby saves another
dynamic method dispatch by hard-coding Array#first to just grab the first
item from the internal data structure -- just like calling Array#[](0)
would, but it's faster. It might even make a noticeable difference in some
application that calls Array#first and #last a lot.. (I don't propose such
cases do exist, but every small part counts)

array.c:
static VALUE
rb_ary_first(int argc, VALUE *argv, VALUE ary)
{
if (argc == 0) {
if (RARRAY_LEN(ary) == 0) return Qnil;
return RARRAY_PTR(ary)[0];
}
else {
return ary_shared_first(argc, argv, ary, Qfalse);
}
}

Here seen retrieving the first item manually.

Arlen

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