CODEWITHSUNDEEP
c++templateslambdac++14
Chenna V
Chenna V

Reputation: 10483

Deduction of auto doesn't work when implemented as Lambda. Error: before deduction of 'auto'

Here I've implemented a templated function and a templated Lambda. I've started exploring C++14 features and not sure what's wrong with the following lambda. Any suggestions?

#include <iostream>
#include <random>
#include <algorithm>
#include <functional>

template<class T = std::mt19937, std::size_t N = T::state_size>
auto MersenneEngine() {
    return T(N);
}

template<class T = std::mt19937, std::size_t N = T::state_size>
auto MersenneEngineLambda = []() {
    return T(N);
};

int main() {
    // your code goes here
    std::cout << MersenneEngine<std::mt19937>() << std::endl;
    std::cout << MersenneEngineLambda<std::mt19937>() << std::endl; // Compilation error : error: use of 'MersenneEngineLambda<std::mersenne_twister_engine...before deduction of 'auto'
    return 0;
}

Here's the complete code http://ideone.com/lveJRN

Upvotes: 0

Views: 231

Answers (1)

Lightness Races in Orbit
Lightness Races in Orbit

Reputation: 385144

The code is fine.

You are witnessing a bug in your version of GCC (5.1). This is not highly surprising given that variable templates were brand new in GCC 5.

Empirically, it was fixed either in or before GCC 6.1.1.

Bug 67041 (and, more directly, its dupe bug 67350) looks potentially relevant.

Upvotes: 4

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