Re: clone and overrides

[Steven Knight]

> I'm trying to create a new cons environment from an existing one, and
> modify some of the variables. I tried the following:
>
> $vm_ta_env = $vm_env->clone(
>   CFLAGS => '-DMISSIONPACK ' . $CFLAGS
>   );

The above would expand the *Perl* variable $CFLAGS, not the environment
construction variable %CFLAGS.  Hence, nothing gets appended.  *If*
clone() expanded construction variables, the way to do it would be:

        $vm_ta_env = $vm_env->clone(
                CFLAGS => '-DMISSIONPACK %CFLAGS'
        );

But clone() doesn't expand construction variables...

> I end up with a $CFLAGS that only holds '-DMISSIONPACK ', I had to find
> another way to get what I wanted:
>
> %vm_ta_env_hash = $vm_env->copy();
> $vm_ta_env_hash{CFLAGS} = '-DMISSIONPACK ' . $vm_ta_env_hash{CFLAGS};
> $vm_ta_env = new cons(%vm_ta_env_hash);

Here's a slightly less roundabout way to do what you want; fetch the
CFLAGS construction variable explicitly:

        $vm_ta_env = $vm_env->clone(
                CFLAGS => '-DMISSIONPACK ' . $vm_env->{CFLAGS},
        );

> Is there a reason why the clone() command doesn't override correctly? Or
> is it a bug?

It overrides "correctly," it's just never been defined to expand
construction variables within the overridden values.  That would be an
attractive enhancement.

        --SK