Workarounds and Alternatives
While the convention is to place template implementations in header files, there are workarounds and alternatives if separation of declaration and implementation is desired. One common approach is to use the “export” keyword, but it is not widely supported by compilers, and its usage can be complex. Another alternative is explicit instantiation, where specific instantiations of the template are explicitly declared in the source file.
// header file: mytemplate.h
template <typename T>
T add(T a, T b);
// source file: mytemplate.cpp
#include "mytemplate.h"
template int add<int>(int a, int b);
// source file: main.cpp
#include "mytemplate.h"
int main() {
int result = add(5, 10);
return 0;
}
However, these alternatives come with their own set of complexities and potential pitfalls.
Why can templates only be implemented in the header file?
Templates are a powerful feature in C++ that allows for the creation of generic functions and classes. They provide a way to write code that works with different data types without sacrificing type safety. However, one notable restriction when working with templates is that their implementation is often required to be in the header file. This limitation arises due to the way C++ templates are compiled and instantiated.