Modules 100% solve this problem, but broad compiler support is still (frustratingly) lacking.
Some day, a class like in the OP will be implementable in a single file. The compiler will compile that once, and users can 'import' it infinitely without worrying about the usual header inclusion pitfalls, and without incurring any compile time overhead. The amount of electricity saved from the reduced compilation work will save us from the current climate disaster, and we'll become a maximally productive society unburdened by slow C++ compilers.
Some day, a class like in the OP will be implementable in a single file. The compiler will compile that once, and users can 'import' it infinitely without worrying about the usual header inclusion pitfalls, and without incurring any compile time overhead. The amount of electricity saved from the reduced compilation work will save us from the current climate disaster, and we'll become a maximally productive society unburdened by slow C++ compilers.