Re: [Dev-C++] Is it possible - templates (.h and .cpp) ?

[Kevin B. <kev...@ma...>]

>This makes it impossible to use templates without letting the
>compiler see the full declarations for the template.

Not entirely accurate. The C++ standard does, in fact, specify a facility 
for separate compilation of template code, using the export keyword.

Unfortunately, there is almost no compiler support for this yet. In fact, 
to my knowledge only the EDG compiler supports it in any reasonably 
complete way. So, as a practical matter, it remains close to impossible for 
the immediate future.

But, it is standard C++, and so eventually, anybody who wants to pretend to 
compliance will support it.

Meanwhile, you can still divide your code into .h and .cpp, and merely use 
some conditional compilation to accomodate non-compliant compilers, 
something like so:

// Global definition somewhere
#if defined(USE_EXPORT)
#define EXPORT export
#else
#define EXPORT
#endif

// mytemplate.h

EXPORT
template<class T>
...whatever...

#if !defined(USE_EXPORT)
#include mytemplate.cpp
#endif

In this way, you can divide your code, it'll work now, and you'll be ready 
for the future.


Another option is to use explicit instatiation. This allows you to hide 
your implementation completely without all the preprocessor nonsense above, 
and still satisfy the linker by explicitly instatiating whatever various 
examples of the template your program happens to require. This can be a 
maintenance headache, though, since you need to keep track of what template 
variations are used by the rest of your program.

/* mytemplate.cpp */
#include "mytemplate.h"

// Implement template here.

// Instatiate myclass for int and float,
// which is all we use in the whole program.
template myclass<int>;
template myclass<float>;



--- Kevin