Remember that

sub foo(&);
foo { ... };
[download]

is syntax sugar for

foo(sub { ... });
[download]

On the other hand, the block for map is no more a sub than the block for for.

use strict;
use warnings;

sub my_map(&@) {
    my $cb = shift;
    my @rv;
    push @rv, $cb->($_) for @_;
    return @rv;
}

sub map_tester {
   print("pre\n");
   map { print("in\n"); return 1 } 1;
   print("post\n");
}

sub my_map_tester {
   print("pre\n");
   my_map { print("in\n"); return 1 } 1;
   print("post\n");
}

map_tester();
print("\n");
my_map_tester();
[download]

pre
in

pre
in
post
[download]

Why the difference in behavior?

The only existing means of calling a detached (e.g. referenced) opcode tree is a sub.

That's true even at a very low level. That's why map isn't implemented as a function that takes the block as an argument. map is truly a flow control structure.

For example, @b = map { foo() } @a compiles into something like the following:

my @anon_list;
for (@a) {
    push @anon_list, foo();
}
@b = @anon_list;
[download]

There's obviously no way to compile a call my_map into a loop, so differences are to be expected.

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