Equivalents of C++ 2016 "if statement with initializer", in Perl 5

if-statement-with-initializer.pl

# Equivalents of C++ 2016 "if statement with initializer", in Perl 5
# http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0305r0.html
#

if ((my $p = $m->try_emplace($key, $value)), !$p->second) {
    FATAL("Element already registered")
} else {
    process($p->second)
}

sub foo() {
    if ((my $c = bar()) != SUCCESS) {
        return $c
    }
    ...
}

# Other examples
if ((my $x = 0) != 0) {
    say $x
} else {
    say $x-1
}
# Unfortunately, $x escapes the "if" block, so this is not as strict as C++.
say $x