Re: [Boost-users] error using lambdas: conversion from 'x' tonon-scalar type 'y'

4 Jul 2006


      Peter Dimov wrote:
...
klaus triendl wrote:
[...]
...
MyStream& operator <<(MyStream& os, const int&)
{
  return os;
}
int main()
{
  list cont;
  MyStream osTop;
  MySubStream osSub(&osTop);
MyStream& tmp = osSub;
...
for_each(cont.begin(), cont.end(), ref(osSub) << *_1);
for_each( cont.begin(), cont.end(), tmp << *_1 );
// or, if the above doesn't work - it should -
for_each( cont.begin(), cont.end(), ref(tmp) << *_1 );
...
return 0;
}
----
g++ outputs error:
'/usr/include/boost/lambda/detail/operator_lambda_func_base.hpp:212:
error: conversion from 'MyStream' to non-scalar type 'MySubStream'
requested'.
Lambda sees that you are invoking operator<< on a MySubStream& and deduces 
the return type to be MySubStream&; it isn't smart enough to see that you're 
actually using the operator<< definition for the base class MyStream.
I thought that it would be converted implicitly in the end by the compiler..
Can I make it smart enough?


--
Klaus