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 $_ is readonly isn't a possible solution?
For one thing, then you couldn't do this:
my @a = 1, 2, 3;
for @a {
++$_;
}
// Carl
