S06: Pairs as lvalues - perl.perl6.language

Message from discussion S06: Pairs as lvalues

Luke Palmer

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More options Feb 26 2005, 6:03 pm

Newsgroups: perl.perl6.language

From: l...@luqui.org (Luke Palmer)

Date: Sat, 26 Feb 2005 16:03:21 -0700

Local: Sat, Feb 26 2005 6:03 pm

Subject: Re: S06: Pairs as lvalues

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Ingo Blechschmidt writes:
> that's really convenient, but what will the following code do?
> my $x = (a => 42); # $x is a Pair.
> $x = 13; # Is $x now the Pair (a => 13) or
> # the Int 13?

It's the Int 13. Your example looks a lot like this one:

my $x = [ 1, 2, 3 ];
$x = 13;

And you could say that is an error because:

[ 1, 2, 3 ] = 13;

Is an error, but you'd be wrong. You see, in your example, the pair is
not "functioning as an lvalue". The variable is the thing that is the
lvalue, not the pair.

I belive you could get the pair as an lvalue if you did:

my (Pair $x) := (a => 42);
$x = 13;

Because the variable x is now *fundamentally* a pair; it has no
container, so to speak. But it would die, because you're trying to
change a constant value.

Luke

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