daz
9/13/2003 12:38:00 PM
"Michael Garriss" <mgarriss@earthlink.net> wrote:
> Michael Garriss wrote:
>
> > Is this code guaranteed to always work this way:
> >
> > a = [1,2,3,4,5]
> > --> [1, 2, 3, 4, 5]
> > def m( a, b, *c )
> > puts a, b, c
> > end
> > --> nil
> > m( a.shift, a.shift, a )
> > 1
> > 2
> > 3
> > 4
> > 5
> > --> nil
> >
> > I''m wondering (hoping) that the arguments will always be evaluated
> > from left to right as is the case above. Is this a ''ruby rule'' or
> > something that could change?
> >
From Pickaxe:
The Ruby Language
Method Definition
Method Arguments
(I can''t find this section on rubycentral/book to link to)
"The expressions are evaluated from left to right.
An expression may reference a parameter that precedes it
in the argument list."
#--------------------
a = [1,2,3,4,5]
def m( a, b, *c )
p a, b, c
end
m( a.shift, b=a, a )
#--------------------
#-> 1
#-> [2, 3, 4, 5]
#-> [[2, 3, 4, 5]]
So that''s as safe as Pickaxe.
>
> Let me extend the question to include arrays (which might
> be related to arguments, I don''t know, I''ve never looked
> at the ruby source):
>
> a = [1,2,3,4,5]
> --> [1, 2, 3, 4, 5]
> b = [a.shift,a.shift,a.shift,a.shift,a.shift]
> --> [1, 2, 3, 4, 5]
>
Well, since:
a, b = b, a
is ''defined'' (in the sense that it''s a ruby idiom),
your example works the way I''d expect, even though
Matz has guarded his options. Perhaps he means that
this could look like a prime candidate for optimization
which would give [1, 1, 1, 1, 1] but I don''t know if
anyone would like to see that happen.
>
> Michael
>
daz