Re: [boost] [proto] docs unclear (to me) for: "Expression Nodes as Fusion Sequences"

11 Mar 2008


      Markus Werle wrote:
...
Hi!
In the section "Expression Nodes as Fusion Sequences"
you show the follwing code
struct fun_t {};
terminal<fun_t>::type const fun = {{}};
// ...
fusion::for_each(
    fusion::transform(
        // pop_front() removes the "fun" child
        fusion::pop_front(fun(1,2,3,4))
        // Extract the ints from the terminal nodes
      , functional::arg<>()
    )
  , display()
);
It did not became clear to me why a terminal<fun_t>::type 
can be initialized with 4 integer arguments.
"fun" is an object. It is already initialized.
...
I thought terminal<fun_t>::type is equivalent to 
expr< tag::terminal, args0< fun_t >, 0 >
and should take no args at all.
Could you clarify this?
"fun(1,2,3,4)" is an invocation of an overloaded function call operator. 
Proto is an expression template library ... all operators are overloaded 
to build expression trees. This operator builds a tree node representing 
a function invocation.

HTH,

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com