[FIXED] Why would one write a C++ lambda with a name so it can be called from somewhere?

Issue

Why would one write a C++ lambda with a name so it can be called from somewhere? Would that not defeat the very purpose of a lambda? Is it better to write a function instead there? If not, why? Would a function instead have any disadvantages?

Solution

I see three things to consider when choosing between a named lamdba and a free function:

1. Do you need variables from the surrouding scope? If yes, choose a lamdba and leverage its closure. Otherwise, go with a free function (because of 3.).
2. Could the closure state equally well be passed as a function parameter? If yes, consider preferring a free function (because of 3.).

3. Do you want to write a test for the callable and/or reuse it in multiple translation units? If yes, choose a free function, because you must declare it in a header file and capturing variables in a lamdba closure

   • is a bit confusing in a header file (though this is debatable, of course).

   • requires the types to be known. You can't therefore live with forward declarations of function parameters and return types to reduce compilation times.

Answered By - lubgr

Answer Checked By - Clifford M. (PHPFixing Volunteer)