csharp2a has asked for the wisdom of the Perl Monks concerning the following question:

Hello Monks, I have encountered a use of scaler context that has me a bit confused. I would expect the following snippet to actually be a hash however the coder has used the scaler context. If this is correct, would someone be able to help me understand why it would not be a hash? Sorry for the elementary question, but it has caused confusion. 

 my $headers = {
           'Accept'        => 'application/json',
           'Content-Type'  => 'application/json',
           'charset'       => 'UTF-8'
 };

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Thank you.

Replies are listed 'Best First'.
Re: Confused on Scalar/Hash
by toolic (Bishop) on Apr 02, 2018 at 15:33 UTC
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Re: Confused on Scalar/Hash
by stevieb (Canon) on Apr 02, 2018 at 15:34 UTC

    That's a scalar that contains a reference to a hash.

    Observe (untested):

    my %hash = (
    a => 1,
    b => 2,
);

my $href = \%hash;

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    The coder just skipped the intermediary step of taking a reference to the hash, and instead constructed it as a hash reference directly. To get information from the hash as I depicted above, you access it normally:

    my $thing = $hash{a};

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    In the case of the hash reference, you have to dereference first:

    my $thing = $href->{a};

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    You can dereference the entire hash reference and put it into a new hash if you please, but there's not often reason to do so unless you need a copy of the entire structure:

    my %hash = %{ $href };

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    See perlreftut.

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Re: Confused on Scalar/Hash
by AnomalousMonk (Archbishop) on Apr 02, 2018 at 16:05 UTC
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Re: Confused on Scalar/Hash
by csharp2a (Novice) on Apr 02, 2018 at 15:57 UTC
    Now I see it. It makes complete sense. I was not aware that you could use this method. Something new for my coding bag of tricks. Thank you all for the excellent explanations! Craig
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Re: Confused on Scalar/Hash
by LanX (Saint) on Apr 02, 2018 at 15:41 UTC
    I personally understand %hash as the "list form" of a hash.

    You assign lists and you get lists of elements.

    i.e. %hash2 = %hash will copy the lists of key-value pairs into a new hash.

    $hash_ref = \%hash is a pointer to the container.

    $hash_ref2 = $hash_ref will share the same hash.

    changing $hash_ref2->{a}++ will also effect $hash_ref

    Many other languages only know the reference form. Like in JS hash={...} is a hash_ref.

    HTH!

    Cheers Rolf
    (addicted to the Perl Programming Language and ☆☆☆☆ :)
    Wikisyntax for the Monastery

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Re: Confused on Scalar/Hash
by Anonymous Monk on Apr 02, 2018 at 16:47 UTC
    You have no doubt heard the terms, "hashref" and "arrayref," being bantered-about here. Now you know.
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      The kid you take off the bench to play for the last 90 seconds of the game when you're winning by 24 points.

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      You have no doubt heard the terms, "hashref" and "arrayref,"...

      Actually, nope, nobody but yourself has mentioned "arrayref" in this entire thread ;)

      /pedantic

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