Moritz (>), Solomon (>>), Moritz (>>>):
>> > the current spec doesn't allow immutable containers to call .map with a
>> > block that implicitly uses $_ as an implicit parameter.
>> >
>> > Here's why:
>> >
>> > S06 says
>> >
>> >> The C<$_> variable functions as a placeholder in a block without any
>> >> other placeholders or signature. Any bare block without placeholders
>> >> really has a parameter like this:
>> >>
>> >> -> $_ is rw = OUTER::<$_> { .mumble }
>> >
>> > So $_ is marked as rw, which is checked at binding time.
>> >
>> > Now lists are immutable, meaning that you can't bind a list item rw, so
>> > even if the block doesn't try to modify $_, calling the { .say } block
>> > fails.
>> >
>> > (Note that 'for' has the same problem)
>> >
>> > How should that be resolved? Should a temporary variable be created that
>> > can be changed, without any effect? or should it fail() on detecting a
>> > modification? Somehow this approach seems very backward to me...
>>
>> Is there a reason $_ is readonly isn't a possible solution?
>
> I have no idea how often $_ as an implicit parameter is actually used.
> Note that if you want s/// to work, you really need a mutable $_.
>
> If it were just for iteration, I'd not object to making it an ro-alias by
> default, requiring an explict rw signature (for example with <-> $_ { ... })
> otherwise.
That would make statement modifier for loops less useful. For those,
there's nowhere to put the lambda arrow.
++$_ for @things;
// Carl
