[cfe-dev] Dynamic / Last Resort Lookup

[Axel Naumann]

Hi,

We need to implement something similar to dynamic scopes:

void f() {
  File::Open("serialized.data");
  object->func();
}

This will call func() on an object that was retrieved from the file
serialized.data (all of it happens at runtime). The part that blocks us
from implementing it is Sema: all the lookup hooks require a predefined
set of identifiers.

Attached patch creates a last resort, dynamic lookup: if that hook
(implemented by an abstract interface) has been provided, it will get
its chance to look up a symbol but only if all the other language
foreseen lookups have failed (i.e. with lowest precedence).

We believe that the cost for clang is minimal, but for us the benefit
would be huge. Any chance that I may check it in? Of course better ideas
and / or suggestions for naming improvements are very welcome :-)

Cheers, Axel.
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