in reply to References for ano subs fixed at compile time?

Here's how it it works. Consider the following code: 
$f = sub { .... };

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At compile time, the code within {} is compiled into a prototype anonymous sub (CV), which is squirrelled away somewhere. At run time, the action of sub {...} is to make a copy of that sub (allocating a new CV), and then return a reference to that new CV.

As an optimisation, if the sub isn't a closure, then rather than copying the CV, a reference is just returned to the original prototype CV. This optimisation isn't perfect; in particular if one blesses $f, then the prototype CV gets blessed, and any new executions of that $f = sub {...} assignment get a blessed coderef.

Finally, note that perl maintains a pool of spare CVs; when one is freed, it gets returned to the pool and that may get reused soon.

Of course, these are implementation details which are subject to change.

Dave.

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Re^2: References for ano subs fixed at compile time?
by ikegami (Patriarch) on Jun 20, 2013 at 07:30 UTC
    Demonstration: 
    sub f(&) { my ($cr) = @_; push @keep_alive, $cr; say $cr; }

my $x = '...';

f { '...' } for 1..2;
f { $x }    for 1..2;

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    CODE(0x3396f4)  \ same for non-capturing
CODE(0x3396f4)  /
CODE(0x24b1cc)  \ different for capturing
CODE(0x338c04)  /

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