I find the desired short cut behaviour to catch undef even more problematic than the rest.

I'd rather prefer a catch_undef { BLOCK } command, because the block would be explicit about what is caught without much explanation.

This can be emulated (at least) with

my $h_b = {};
my $x   = eval {
    use warnings FATAL => 'uninitialized' ;
    $h_b->{velocity}." mph";
} // 'unknown';

print $x;
[download]

I tried to construct some syntactic sugar

sub catch_undef (&) {
    my $code_ref = shift;
    
    eval {
        use warnings FATAL => 'uninitialized' ;
        $code_ref->()
    };
}
[download]

but I'm running into two problems:

1) Obviously pragmas are lexically scoped, I seem to remember there are some obscure tricks to manipulate the warning flags of a coderef (something with $^H ?) but I'm too lazy at the moment.

2) seems to be a bug in the parser, because I get a weird syntax error for

 catch_undef { $ref->{velocity} .'mph' }  //  "unknown";

Too many arguments for main::catch_undef at /tmp/tst.pl line 29, near "//  "unknown""

using || instead solves the parsing problem (but not the task)

I'd rather prefer a catch_undef { BLOCK } command, because the block would be explicit about what is caught without much explanation.

While throwing exceptions or returning early from subroutines are indeed ways of taking short-cuts, it is tricky to get the amount of control I am looking for with existing language constructs.

Keep in mind that the suggested operator does not need something that would trigger a warning or error to work, nor would it change the behaviour of similar warnings in the same block.

The method calling chain $a->foo->bar^^->baz->qux, say, would give us a short-cut after bar() but nowhere else. Likewise, the dereferencing chain $a->[1]->[2]^^->[3] would autovivify $a->[1] but not $a->[1]->[2].