[boost] [Boost-bugs] [ boost-Bugs-1602075 ] Lambda: (_1 + "y")(string("x")) Doesn't Compile

From: SourceForge.net (noreply_at_[hidden])
Date: 2006-11-23 22:14:31

Bugs item #1602075, was opened at 2006-11-23 19:14
Message generated for change (Tracker Item Submitted) made by Item Submitter
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Nobody/Anonymous (nobody)
Summary: Lambda: (_1 + "y")(string("x")) Doesn't Compile

Initial Comment:
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.

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