Proto for Boost mailing list page: [proto] Flags expression as being "top level"

Subject: [proto] Flags expression as being "top level"
From: Joel Falcou (joel.falcou_at_[hidden])
Date: 2011-04-03 11:29:56

Hello,

we need a way to know if a given expression is the "top level" one.
The use case is to detect the last = in expression like:

a = b = c = x * y;

A working but runtime version is given as : http://codepad.org/MO2NUgI2

Havign this feature at compiel time sounds a lot better. I think it 
requires to
have a expression type carrying a bool_ in its type. Thus in the generator,
we set this bool_ to false_ in incoming expression and put it back into the
newly generated expression.

Is this a correct way of doing this or is there somethign already in 
proto we missed ?

Regards