Eric Niebler a écrit :
The first question to ask is if it is really absolutely necessary to prevent users from creating invalid expressions with my_custom_binary_func(), or if you can catch the error someplace else; e.g., when users try to evaluate the expression. Reporting a hard error later can often yield a better error message then using SFINAE to prune overload sets earlier. OK then, but I don't really want my user face a large template error because they mismatched some binary function arguments when they can have a nice 'no such function F(A,B)' error message instead.
The solution of enumerating the (expr,expr) (expr,scalar) (scalar,expr) variants is maybe what's needed then ? The only problem I see is that enumerating the ternary one will be real long.
If you want to improve compile times even more, you can avoid make_expr entirely and code by-hand what make_expr would do. So, e.g., the second overload above would be: <snip> Why is this faster than calling make_expr ? Even worse, doesn't it defeat the proto purpose ? Or am I in a situation I have to write dirty code like this and only use Proto as a expression builder ?
-- ___________________________________________ Joel Falcou - Assistant Professor PARALL Team - LRI - Universite Paris Sud XI Tel : (+33)1 69 15 66 35