Lambda: (_1 + "y")(string("x")) Doesn't Compile

[nobody]

This program:

#include <iostream>
#include <ostream>
#include <string>
#include <boost/lambda/lambda.hpp>

int main() {
    const std::string s("Hello");

    std::cout << (boost::lambda::_1 + ", world!")(s) << std::endl;
}

fails to compile with Boost 1.33.1 (on GCC 3.4.2 and GCC 4.1.1, at least) due to at least two bugs.

One bug is in boost/lambda/detail/operators.hpp, lines 269-271. This function, declared to return a lambda_functor, returns a lambda_functor constructed from a tuple. But there is no such constructor. Instead, 'lambda_functor<' should be deleted from line 269 (and the closing '>' from line 271) so that it returns a lambda_functor_base constructed from a tuple. That constructor (which is explicit) does exist, and so does a lambda_functor constructor (which is implicit) from a lambda_functor_base. This is exactly what the macro BOOST_LAMBDA_PTR_ARITHMETIC_E2 immediately below does, and there is no reason for BOOST_LAMBDA_PTR_ARITHMETIC_E1 to be different.

Unfortunately, fixing that leaves another, more complicated bug: for some reason, the return type appears to be deduced as const char * instead of std::string. See for yourself.

[Steven Watanabe]

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I have submitted a patch for this and a few other things to the mailing list.

[nobody]

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Steven Watanabe's updated patch allows this test case to compile and run successfully. Thanks! Please commit it for 1.34.0.

[Steven Watanabe]

(In [50516]) Add specializations of plain_return_type_2 for std::string. Fixes #781