I found myself writing code like this:
template <class T>
inline bool allequal(T a,T b,T c) {return a==b&&a==c;}
template <class T>
inline bool allequal(T a,T b,T c,T d) {return a==b&&a==c&&a==d;}
template <class T>
inline bool allequal(T a,T b,T c,T d,T e) {return a==b&&a==c&&a==d&&a==e;}
I was wondering if there is an automated way of doing that, without using vectors or variadic arguments, as speed is important in this context.
You could try this:
#include <iostream>
template< typename T >
inline bool allequal( const T& v )
{
return true;
}
template< typename T, typename U, typename... Ts >
inline bool allequal( const T& v, const U& v1, const Ts&... Vs)
{
return (v == v1) && allequal( v1, Vs... );
}
int main()
{
std::cout << std::boolalpha;
std::cout << allequal(1, 1, 1, 1) << std::endl;
std::cout << allequal(1, 1, 2, 2) << std::endl;
return 0;
}
AFAIK there is a proposal for C++17 to include custom expansion of variadic templates with operators that could avoid this kind of recursion and this ugly (IMO) termination with return true for one argument.
Note: this could possibly not be inlined for many arguments.
va_args
(1, 1, 2, 2) and fail to compile for (1, 2, 3). Did you mean allequal(v1, Vs...) (and a recursion stopper with one argument)?
all_same to return false; if types are differents.((v == Vs) && ...) (and omit v1); more details here. clang 3.6 accepts it with std=c++1z; I'm not sure about gcc 5 (4.9 does not).#include <algorithm>
#include <iterator>
template <typename T, typename... Args>
bool allequal(T a, Args... rest)
{
std::initializer_list<T> values = {a, rest...};
return std::adjacent_find(begin(values), end(values), std::not_equal_to<T>()) == end(values);
}
not_equal_to, it will bail early without iterating the through the remaining elements. But so will the recursive methods.template<typename First, typename Second>
bool AllOf(First a, Second b)
{
return a == b;
}
template<typename First, typename Second, typename... Rest>
bool AllOf(First a, Second b, Rest... r)
{
return a == b && AllOf(b, r...);
}
std::cout << AllOf(1, 1,1,1) << "\n";
std::cout << AllOf(1, 1,2) << "\n";
std::cout << AllOf(1,2) << "\n";
std::cout << AllOf(1,1) << "\n";
va_arg, I guess.