Question

.inl files are never mandatory and have no special significance to the compiler. It's just a way of structuring your code that provides a hint to the humans that might read it.

I use .inl files in two cases:

For definitions of inline functions.
For definitions of function templates.

In both cases, I put the declarations of the functions in a header file, which is included by other files, then I #include the .inl file at the bottom of the header file.

I like it because it separates the interface from the implementation and makes the header file a little easier to read. If you care about the implementation details, you can open the .inl file and read it. If you don't, you don't have to.

Accepted Answer

.inl files are never mandatory and have no special significance to the compiler. It's just a way of structuring your code that provides a hint to the humans that might read it.

I use .inl files in two cases:

For definitions of inline functions.
For definitions of function templates.

In both cases, I put the declarations of the functions in a header file, which is included by other files, then I #include the .inl file at the bottom of the header file.

I like it because it separates the interface from the implementation and makes the header file a little easier to read. If you care about the implementation details, you can open the .inl file and read it. If you don't, you don't have to.