Inline keyword in member function definition

c++

Solution

`inline` has some pre-historic use, but nowadays it's best to remember it as saying: "this definition is going to be defined multiple times, and that's okay."

That is, normally the one-definition rule prohibits multiple definitions of a function. This:

// foo.hpp
void foo() { /* body */ }

// a.cpp
#include "foo.hpp"

// b.cpp
#include "foo.hpp"

results in an error, as `foo` is defined in two translation units. You can declare things as often as you want. This:

// foo.hpp
void foo();

// foo.cpp
void foo()
{
    /* body */
}

// a.cpp
#include "foo.hpp"

// b.cpp
#include "foo.hpp"

is fine, as `foo` is defined once, and declared multiple times. What `inline` does is allow this:

// foo.hpp
inline void foo() { /* body */ }

// a.cpp
#include "foo.hpp"

// b.cpp
#include "foo.hpp"

to work. It says "if you see `foo` more than once, just assume they are the same and be okay with it".

Problem

Original source