Typeof woes

[H. S. Teoh]

On Wed, Aug 21, 2013 at 02:24:18AM +0200, Andrej Mitrovic wrote:
> On 8/21/13, H. S. Teoh <hsteoh at quickfur.ath.cx> wrote:
> > and typeof(this.Smth) is invalid because this.Smth is already a
> > type, so you can't apply typeof to it.
> 
> I am beginning to wonder if typeof(typeof(expr)) is worthy of an
> error. Would we end up having any bugs if we were to allow typeof() to
> work on types (IOW it would just alias itself to the type)?
> 
> I guess the only way to find out is to try it out in a compiler
> branch, but I'm genuinely curious.

Hmm.

If typeof were idempotent on types, then it would provide nice closure
properties (as in mathematical closure, not delegates) if we ever
implement the proposed typetuple/std.typecons.Tuple unification from the
other thread:

	typeof(tup(1,"a")) == tup(int,string)
	typeof(tup(int,"a")) == tup(int,string)
	typeof(tup(int,string)) == tup(int,string)

This alleviates one of the nagging problems with mixed tuples that
contain both types and expressions. Then the only left to do is to
specify that a tuple can be used as a type only if it contains only
types (IOW, if is(typeof(tup)==tup), a rather nice way to express it),
and a tuple can be used as a value (assigned to variables, etc.) only if
it contains only values.

"Mixed" tuples can still be used as template arguments, and you can
always apply typeof to them.


T

-- 
It's bad luck to be superstitious. -- YHL