Is there a way to write make_unique() in VS2012?

Question

Herb Sutter propose a simple implementation of make_unique() there: http://herbsutter.com/gotw/_102/

Here it is:

template

        

Answer 1

You could use Boost.Preprocessor to generate the different parameter counts, but I really don't see the advantage of that. Simply do the grunt job once, stuff it in a header and be done. You're saving yourself compile time and have your make_unique.

Here's a copy-paste of my make_unique.h header that simulates variadic templates for up to 5 arguments.

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Since OP seems to not like copy-paste work, here's the Boost.Preprocessor code to generate the above:

First, make a main header that includes the template header multiple times (Boost.Preprocessor iteration code blatantly stolen from this answer):

// make_unique.h
#include 
#include 
#include 

#ifndef MAKE_UNIQUE_NUM_ARGS
// allow this to be changed to a higher number if needed,
// ten is a good default number
#define MAKE_UNIQUE_NUM_ARGS 10
#endif

#if MAKE_UNIQUE_NUM_ARGS < 0
// but don't be stupid with it
#error Invalid MAKE_UNIQUE_NUM_ARGS value.
#endif

/* optional, see above for premade version
// include premade functions, to avoid the costly iteration
#include "detail/blah_premade.hpp

// generate classes if needed
#if MAKE_UNIQUE_NUM_ARGS > MAKE_UNIQUE_NUM_PREMADE
*/
#define BOOST_PP_ITERATION_LIMITS (0, MAKE_UNIQUE_NUM_ARGS)
#define BOOST_PP_FILENAME_1 "make_unique_template.h"
#include BOOST_PP_ITERATE()
//#endif

And now make a template header that gets included again and again and expands differently depending on the value of MAKE_UNIQUE_NUM_ARGS:

// make_unique_template.h
// note: no include guard

#define N BOOST_PP_ITERATION()    

#define MAKE_UNIQUE_TEMPLATE_PARMS \
  BOOST_PP_ENUM_PARAMS(N, typename A)

#define MAKE_UNIQUE_FUNCTION_PARM(J,I,D) \
  BOOST_PP_CAT(A,I)&& BOOST_PP_CAT(a,I)

#define MAKE_UNIQUE_FUNCTION_PARMS \
  BOOST_PP_ENUM(N, MAKE_UNIQUE_FUNCTION_PARM, BOOST_PP_EMPTY)

#define MAKE_UNIQUE_ARG(J,I,D) \
  std::forward(BOOST_PP_CAT(a,I))

#define MAKE_UNIQUE_ARGS \
  BOOST_PP_ENUM(N, MAKE_UNIQUE_ARG, BOOST_PP_EMPTY)

template
std::unique_ptr make_unique(MAKE_UNIQUE_FUNCTION_PARMS){
  return std::unique_ptr(new T(MAKE_UNIQUE_ARGS));
}

// clean up
#undef MAKE_UNIQUE_TEMPLATE_PARMS
#undef MAKE_UNIQUE_FUNCTION_PARM
#undef MAKE_UNIQUE_FUNCTION_PARMS
#undef MAKE_UNIQUE_ARG
#undef MAKE_UNIQUE_ARGS
#undef N