Template instantiation saves us from infinite compilation times because whenever you modify a header, the build system (correctly) rebuilds everything that includes that header.
They can also save object size (and likely a little bit of time) because templates are re-instantiated for each object file, unless users mark it as extern on every file, which they won't remember to do
- https://stackoverflow.com/questions/8130602/using-extern-template-c11/59614090#59614090
- https://stackoverflow.com/questions/2351148/explicit-instantiation-when-is-it-used
- https://en.cppreference.com/w/cpp/language/class_template#Explicit_instantiation
We can also confirm with nm -C that the main.o object file does not contain a definition of MyClass, in that case because MyClass is not a complete definition because f is not defined.