Re: [Boost-users] Aliased parameters in boost::bind

Subject: Re: [Boost-users] Aliased parameters in boost::bind
From: Gavin Lambert (gavinl_at_[hidden])
Date: 2017-03-29 22:12:01

On 30/03/2017 06:46, Evgeny Fraimovitch via Boost-users wrote:
> For instance, given the function:
> void f(std::string x, std::string y, std::string z) {
> 	std::cout << x << y << z;
> }
> One could following the tutorial naively write:
> auto triple = boost::bind(f, _1, _1, _1);
>
> and this would even work for:
> std::string x = "a pretty long string";
> triple(x);
> printing the string thrice, as expected.
> However the result of triple(std::string("a pretty long string")) would be
> the string only printed once, which is hardly what the user would expect.
> In fact, any bind expression produced with aliasing would be sensitive to
> the type of the reference passed, violating the functor abstraction badly.

Why would you declare f as copying its parameters by value instead of 
taking them by const& instead?  const& parameters would be safe in this 
case.

const& parameters should be your default for anything with non-trivial 
copy/move behaviour anyway, so you'd only run into this issue in 
already-bad code.

Although it would be nice if there were some way to emit a compiler 
warning for this sort of construct, I agree.