I'm trying to make a function which finds the minimum element in a range which satisfies a given condition:
#include <functional>
#include <iostream>
#include <vector>
template <typename It, typename Pred, typename Comp>
It minElementWhere(
It begin,
It end,
Pred pred = Pred(),
// Use less-than as the default comparator.
Comp comp = std::less<decltype(*std::declval<It>())>()
) {
It minElement = end;
for (It it = begin; it != end; ++it) {
if (!pred(*it)) {
continue;
}
if (comp(*it, *minElement)) {
minElement = it;
}
}
return minElement;
}
int main() {
std::vector<double> foo;
foo.push_back(6);
foo.push_back(10);
foo.push_back(-3);
foo.push_back(7);
std::cout << *minElementWhere(
foo.begin(),
foo.end(),
[](double val) {
return val >= 0;
}
) << std::endl;
}
But I get this error:
main.cpp: In function 'int main()':
main.cpp:40:5: error: no matching function for call to 'minElementWhere(std::vector<double>::iterator, std::vector<double>::iterator, main()::__lambda0)'
) << std::endl;
^
main.cpp:40:5: note: candidate is:
main.cpp:6:4: note: template<class It, class Pred, class Comp> It minElementWhere(It, It, Pred, Comp)
It minElementWhere(
^
main.cpp:6:4: note: template argument deduction/substitution failed:
main.cpp:40:5: note: couldn't deduce template parameter 'Comp'
) << std::endl;
Comp
isn't the return type, so it's not trying to deduce the return type, and it doesn't seem to me like there are ambiguous overloads of Comp
(since there can only be one return type of dereferencing an It
). Why am I getting this error, and how can I fix it?
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