On Sep 27, 2010, at 5:56 AM, John McCall wrote:
> On Sep 20, 2010, at 6:30 PM, Douglas Gregor wrote:
>> I'd really rather not add a new expression type just for the purpose of
>> type-checking __is_convertible_to. How about we synthesize appropriate
>> expressions instead, e.g., a DeclRefExpr to a synthesized variable, or a
>> CallExpr to a synthesized function with an appropriate return type?
>
> Actually, I think there are several places in the AST where "opaque
> expression of fixed type and l-valueness" would be very convenient — mostly
> with copies, e.g. with synthesized array copies, caught-exception copies, etc.
Synthesized array copies always have a parameter to hang on to.
Caught-exception copies could do the same, although I admit that it isn't quite
as natural there.
I'm on the fence. I don't like having expression nodes that don't represent
ideas in the language, but there is some messiness in the expression synthesis
we do in Sema. If we're going to have a special expression node kind for
type-checking purposes, I'd rather that it never make its way into the AST, and
perhaps make it impossible to allocate it on the heap, so that it can be
ignored by everything else (e.g., serialization, checker, codegen).
- Doug
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