How can I disable constant folding in Perl?

Question

Given a command like,

perl -MO=Deparse -E'use constant FOO => 42; print FOO()'

How can I disable constant folding such that

print 42;

Shows me

print FOO();

Or the like. Ideally, I would like this to be a compiler option that works for all of Perl. You can see this talked about in this thread on the perl mailing list, [perl #97942] [PATCH] Add -DO option to disable optimizations and disable constant folding and the peephole optimizer when used.. I tried -DO and it didn't work. If that option doesn't work, I'm open to workarounds however they may come.

Answer 1

One method you can do is to prefix the constant with &,

perl -MO=Deparse -E'use constant FOO => 42; print &FOO()'

From the docs on perldoc perlsub

Constant Functions Functions with a prototype of "()" are potential candidates for inlining. If the result after optimization and constant folding is either a constant or a lexically-scoped scalar which has no other references, then it will be used in place of function calls made without &. Calls made using & are never inlined.