From: Jean-Hugues ROBERT <jean_hugues_robert@...>
Date: 2004-04-29T04:30:29+09:00
Subject: Re: Array to Hash

At 01:12 29/04/2004 +0900, you wrote:
>On 0424, Florian Gross wrote:
> > pair, (key, value) = ["one", 1], ["two", 2]
> > pair  # => ["one", 1]
> > key   # => "two"
> > value # => 2
>
>Why _cannot_ I simply say?
>pair, [key, value] = ["one,1],["two",2]
>[] is for arrays, () is for tuples.

Why, yeah, Why ?

In the context of a lvalue (something at the left of
the assignment operator), you must provide a lvalue,
instead of a value.

It is easy to build values, included nested one using
[]. But only the compiler can build a lvalue.

Probably for historical reasons, the compiler wants
parenthesis within lvalue. And infer the missing
outer ones when it encounter a , before =.

I suppose that the reason is related to the syntax
for formal argument description:
def meth( a, b, c)
end

As a result
def meth( a, [b1,b2], c) looks unbalanced compared to
def meth( a, (b1,b2), c) that Ruby requires.

I guess this is why the later syntax was picked, and
propagated up to the = assignment operator.

Note: That syntax applies for Proc's parameters too.

I suppose that there is some true value in that syntax,
because, within (), access to variables is by reference,
not by value.

All of this is the result of evolution.
For sure, something like a, = meth() is not as obvious
as (a) = meth() or, better, [a] = meth().

But that's the way it is, I suppose you have to accept
it.

Yours,

Jean-Hugues



>Gergo
>
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