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Eliminating &{} and *{}

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Autrijus Tang
July 31, 2005 08:33
Eliminating &{} and *{}
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Under my current design of containers (see "definition of containers" on
p6c), there are only Scalar, Array and Hash containers.  This is in
accordance to them being the only first-class data structures that deals
with mutable data storage.

This is similar to JVM's division between scalar data and collection data;
it's just Perl 6 introduces two collections with differnet interfaces.

With the elimination of the * sigil and the *{} dereferencer, the only
unresolved sigil type is &.  Unlike collections, it is really difficult
to tell the difference between $code and &{$code}.  Moreover, it makes
little sense to say:

    tie(&code, TiedCode);

Since it is much easier to just wrap the &code in place.

All this led us to think about whether (my &foo) can be merely treated
the same as (my Code $foo).  The mutable form will enable convenient
notations such as:

    &foo = sub { ... };

So instead of having to explain to newcomers that you cannot assign
to a &-sigil symbol, it would all just work.  Under this view, &{$x}
would be eliminated with *{}.

Another idea is to treat (my &foo) the same way (my Code $foo is constant).
That will discourage people into assigning into functions, and enable
the compiler to detect function variables at lvalue position as errors,
but on the whole I don't think it's worth the complexity.

Does this make sense?

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