[Boost-users] A simple question involving boost.function and boost.lambda

From: gredner_at_[hidden]
Date: 2004-05-19 12:37:12

Greetings,

I would like to crate a lambda expression that simply executes two functions sequentially.  I have:

using namespace boost;
using namespace boost::lambda;
function0<void> func1 = cout << constant('1');
function0<void> func2 = cout << constant('2');

I have tried:
function0<void> funcs = (func1, func2);
but this seems to execute only one of the two functions when it is called.

I have also tried:
function0<void> funcs = (_1(), _2())(func1, func2);
but my compiler (GCC 3.3 under darwin) barfs it up, with error messages:
----------
main.cpp: In function `int main(int, char**)':
main.cpp:58: error: no match for call to `(boost::tuples::null_type) (
   boost::function0<void, std::allocator<boost::function_base> >&,
   boost::function0<void, std::allocator<boost::function_base> >&)'
/usr/local/include/boost-1_31/boost/lambda/detail/lambda_functors.hpp: In
   member function `RET boost::lambda::placeholder<1>::call(A&, B&, C&, Env&)
   const [with RET = boost::tuples::null_type, A = const
   boost::tuples::null_type, B = const boost::tuples::null_type, C = const
   boost::tuples::null_type, Env = const boost::tuples::null_type]':
/usr/local/include/boost-1_31/boost/lambda/detail/lambda_functors.hpp:143:   instantiated 
from `typename T::sig<boost::tuples::null_type>::type 
boost::lambda::lambda_functor<Base>::operator()() const [with T = 
boost::lambda::placeholder<1>]'
main.cpp:58:   instantiated from here
/usr/local/include/boost-1_31/boost/lambda/detail/lambda_functors.hpp:65: error: invalid
   application of `sizeof' to an incomplete type
----------
(line 58 is the assignment to funcs)

I'd appreciate any advice :)

-Gabe Redner