need an explanation

Lennotoecom has asked for the wisdom of the Perl Monks concerning the following question:

Hi, can you explain please
how exactly this snippet works,
and if possible context transformation:

@a = qw(a b c d e);
$b = () = @a;  # $b now is 5
[download]

Thanks!

update:
$b = @a;
would do the same effect,
so basically there is no need for ();
but still, the question remains if someone got
any explanation

update update:
thank you for answer Mr. Choroba
yes indeed that was just the wrong example that was used by some fellow
your last example was helpful
thank a lot

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Re: need an explanation by choroba (Cardinal) on Sep 22, 2013 at 21:55 UTC
The first line is equivalent to `@a = ('a', 'b', 'c', 'd', 'e');` [download] `qw` just "quotes words". The second line is usually written as `$b = @a;` [download] or, for more clarity, `$b = scalar @a;` [download] Perl is sensitive to context. By assigning to a scalar value, you impose the scalar context on the right hand side of the assignment. Arrays return their size (number of elements) in scalar context. Using `= () =` here has no effect and is only confusing. Update: It is usually used to force list context, for example `$x = () = "abcdABCabA" =~ /a/ig; # Count A's regardless of case.` [download] لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply] [d/l] [select]

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Re: need an explanation
by choroba (Cardinal) on Sep 22, 2013 at 21:55 UTC

@a = ('a', 'b', 'c', 'd', 'e');
[download]

qw just "quotes words".

The second line is usually written as

$b = @a;
[download]

or, for more clarity,

$b = scalar @a;
[download]

Perl is sensitive to context. By assigning to a scalar value, you impose the scalar context on the right hand side of the assignment. Arrays return their size (number of elements) in scalar context. Using = () = here has no effect and is only confusing. Update: It is usually used to force list context, for example

$x = () = "abcdABCabA" =~ /a/ig; # Count A's regardless of case.
[download]

لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

[reply]
[d/l]
[select]