Re^12: can sub check context for lvalue vs rvalue context?

[perl-diddler]

In non-lvalue context, you can return the direct variable. It doesn't matter if the lvalue is "ever" modified -- only at that point when it is dereferenced. It isn't returned if you are taking a reference to it.

Only in every instance where you dereference it, does it THEN determine context. But passing around a reference is a null-op as far as the object goes. The code in it won't get called as long as one is only taking references to it and passing them around as references or aliases.

[BrowserUk]

In non-lvalue context, you can return the direct variable. It doesn't matter if the lvalue is "ever" modified -- only at that point when it is dereferenced. It isn't returned if you are taking a reference to it.

Sorry, but I think I've been more than patient. That's BS!

Its BS, because you cannot ever know if it is called "In non-lvalue context". Perl provides no mechanism to give you that information.

Wishing it were so does not make it so. Stridently concluded that "you can"; on the basis of your fantasy that you could if perl gave you the information; is stupid.

Stupid, because Perl cannot give you that information!.

Another attempt. This time, try reading the code and understanding it -- not your fantasy vision of it:

sub x :lvalue{ ...; $something }
...

someFunc( x() );

The value returned from x() is passed to somefunc() as $_[0]; if somefunc() modifies $_[0], it also modifies $something within x(). Perl cannot know if it does!

And someFunc() might do someOtherFunc( $_[0] ); And if someOtherFunc() modifies it's version of $_[0], it will also modify $something in x().

And if someOtherFunc() calls someOtherOtherFunc( $_[0] ); And if someOtherOtherFunc() modifies it's version of $_[0], then it will also modify $something.

And if someOtherOtherFunc()....

It is not possible for Perl to delve into all the calling code; and all the code it calls, and all the code that code calls through to the end of the program run to determine if anything will/could/might modify the lvalue x() returns.

And wish and prevaricate as much as you like; it ain't never gonna happen.