Re: Question about LUA_MASKRET

[RLake@...]

> The Lua manual states:

> "The return hook is called when the interpreter returns from
a function. The hook is called just before Lua leaves the function."

> I noticed that return hooks are executed *after* locals have been
cleared from the function stack, and before the function exits.

That is what the manual says: "just before Lua
leaves the function". 

> Is there a reason why the locals are cleared
before the return hook triggers? 

1) If the return were actually a tailcall, there would
be no practical way to hook before the locals were cleared.

2) There is nothing in principle stopping a Lua interpreter
from overwriting arbitrary locals while computing return values. Defining
a return hook the way you apparently think it should be would preclude
this optimisation.

3) Related to the above point, conceptually there
are no locals at the point where the return is happening (possibly aside
from the function parameters). The _expression_ return statement is executed
after the return values are computed, and there are no remaining locals
in scope after that. This might be clearer if you think of a stack machine
implementation.

If you want to examine the locals before the entire
return statement executes, you should probably use a line hook.

Just one person's opinion, of course...