When we execute my code above, the script throws an exception because &{ 'run' } violates "strict refs". Khen1950fx explained how to avoid this problem (I appreciate his suggestion).

my $walkable = defined &{ 'walk' };
undef &{ 'walk' };
[download]

Well , yes, this part I understood when I answered Re^2: undef/defined &{$name} while "strict refs"

The answer according to strict is that its an exception made for AUTOLOAD

No, here is the relevant quote from the documentation for the strict pragma:

strict refs 

This generates a runtime error if you use symbolic references (see per
+lref).

...

There is one exception to this rule:
    $bar = \&{'foo'};
    &$bar;

is allowed so that goto &$AUTOLOAD would not break under stricture.
[download]

and here is code demonstrating the problem:

>perl -Mstrict -e "sub walk {} sub run {} my $walkable = defined(&{'wa
+lk'}); my $runnable = &{'run'};"
Can't use string ("run") as a subroutine ref while "strict refs" in us
+e at -e line 1.
[download]

So, the question is: How does the documented exception for use strict 'refs', which allows use of a reference to a symbolic sub, explain the observed fact that when defined is applied to the sub itself (not a reference), no runtime error is raised?

Or, conversely: If the expression &{'walk'} is legal as an argument to defined, why is the expression &{'run'} illegal as the right-hand-side of an assignment?

How (and why) does Perl distinguish between these two cases?

Athanasius <°(((>< contra mundum