A sketch of type-safe string formatter using C++11 variadic templates and, unlike fmtlib, focusing on minimal header size & compilation time.

fastformat.hpp

#pragma once

#include <string>

namespace fmt {

#define KIND(X) \
	X(bool,bool) \
	X(signed char,schar) \
	X(unsigned char,uchar) \
	X(char,char) \
	X(wchar_t,wchar_t) \
	X(short,short) \
	X(unsigned short,ushort) \
	X(int,int) \
	X(unsigned int,uint) \
	X(long,long) \
	X(unsigned long,ulong) \
	X(long long,llong) \
	X(unsigned long long,ullong) \
	X(float,float) \
	X(double,double) \
	X(long double,ldouble) \
	X(const void*,voidptr) \
	X(const char*,charptr) \
	X(std::string,string) \
	X(nullptr_t,nullptr)

#define KIND_ENUM(T,V) kind_##V,
enum kind_t { KIND(KIND_ENUM) };
#undef KIND_ENUM

template <typename T> struct type_kind;

#define KIND_SPEC(T,V) template <> struct type_kind<T> { enum { value = kind_##V }; };
KIND(KIND_SPEC)
#undef KIND_SPEC

template <typename T> struct type_kind<T&> { enum { value = type_kind<T>::value }; };
template <typename T> struct type_kind<const T> { enum { value = type_kind<T>::value }; };

#undef KIND

std::string format_impl(const char* spec, const kind_t kinds[], const void* values[], size_t count);

template <typename... Args>
std::string format(const char* spec, Args&&... args)
{
	static constexpr kind_t kinds[] = { kind_t(type_kind<Args>::value)... };
	const void* values[] = { &args... };
	return format_impl(spec, kinds, values, sizeof(kinds) / sizeof(kinds[0]));
}

}