develooper Front page | perl.perl5.porters | Postings from November 2019

Re: Aliasing and Read-only variables

Thread Previous | Thread Next
Paul "LeoNerd" Evans
November 30, 2019 15:52
Re: Aliasing and Read-only variables
Message ID:
On Thu, 28 Nov 2019 17:04:01 +0000
Dave Mitchell <> wrote:

> =head2 :ro

I like this and its semantics, and I like the fact it isn't called
":const", thus saving that for perhaps an even-stronger version one day
that would guarantee no memory mutation (i.e. SV type upgrades), as may
be useful for shared memory or other ideas.


> =head3 Reference Aliasing
> The first type, which I will call "reference aliasing", expects the
> argument to be a I<reference> to something, and the signature
> processing code first dereferences that argument (with dereference
> overloading honoured) and aliases the parameter to the resulting
> container - croaking if it's not a suitable reference. For example:
>     sub foo(\$x, \@a, \%h, $other, $stuff) { ... }
>     foo(\$X, [], \%H, 1, 2);
> Then within the body of foo(), $x is an alias for $X, @a for the
> anonymous array, and %h for %H. This type of aliasing is more useful
> for array and hash references, but scalars are supported for
> completeness. Note that @a and %h are *not* slurpy parameters; they
> consume a single argument, and more parameters can follow them.

An often-overlooked thought - what about ref-aliases to code blocks?

Now we have lexical subs, I wonder if we'd permit the following:

  sub MY_map(\&body, @args) {
    my @ret;
    push @ret, body($_) for @args;
    return @ret;

It seems a simple-enough addition of the idea to ref-alias a
`my sub foo` here.

Paul "LeoNerd" Evans      |  |

Thread Previous | Thread Next Perl Programming lists via nntp and http.
Comments to Ask Bjørn Hansen at | Group listing | About