The subroutine &hello doesn't exist. In fact $::{hello} is &hello's prototype (as a plain string). There's no CV or CV-ish value around yet--just a plain string being the prototype. When you do *hello, \&hello or $hello you create the glob at comile-time and so $::{hello} returns a glob. This means that 

sub hello;
*fh = $::{hello};
*hello;

[download]
works. See Re^3: Grabbing Variable Names for an elaboration.

ihb

See perltoc if you don't know which perldoc to read!

In reply to Re^2: How can I tell if a function has been forward declared but not yet defined? by ihb
in thread How can I tell if a function has been forward declared but not yet defined? by mab

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