Re^4: Check if key exist in hash but not exact match

[ibm1620]

my $fmt = "%-7s %-@{[max map length, keys %$hash]}s ";

Definitely adding this to my snippet file! But I've never seen this syntax before. What is triggering the code evaluation of max(...) here?

[LanX]

> What is triggering the code evaluation of max(...) here?

"  @{[...]}  " is an idiomatic pseudo-operator by combining several mechanisms

• String interpolation work not only for arrays but also for dereferencing of arrays.

  " @{$a_ref} "

• The [...] marks an anonymous array-ref.

  " @{[ 1, 2, 3 ]} "

• Lists can also include code statements to be executed

  " @{[ 1, 2, some_code() ]} "

• The returned list will be included into the string.

    DB<6> p ">>> @{[ 1, 2, time() ]} <<<"
  >>> 1 2 1680647910 <<<
    DB<7>
  

update

added code examples for each step

[eyepopslikeamosquito]

Definitely adding this to my snippet file! But I've never seen this syntax before.

@{[]} is the famous Baby Cart Secret Operator.

I must say I'm shocked LanX didn't mention his visualization of this operator, namely "a guy with sombrero dragging a sled(ge) uphill" ... which is why he usually refers to it as the Mexican Sledge operator.

See also: Secret Operator References

[kcott]

G'day ibm1620,

The @{[...]} construct is one of many that are referred to as "Perl secret operators and constants".

This one, called "Baby cart", has been around for a very long time. Follow that link for an answer to your question as well as other information.

I have been using it since the 1990s and, as I recall, wasn't even aware that it was a perlsecret until much later. I think I first encountered it in one of the "O'Reilly Perl books". I don't remember which one; although, "Advanced Perl Programming" is a likely candidate. Note that's the original edition; "Advanced Perl Programming, 2nd edition" is completely different — a very poor choice of title in my opinion.

[ibm1620]

*contented sigh*

I love Perl.