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Lambdas in various cases of std::apply in xfunction.hpp don't return correct types #2911
Description
After an update from #2876, the following code stopped compiling:
auto values_original = xt::xtensor<double, 1>{ 1., 2., 3. };
auto indexes = xt::arange<size_t>(values_original.size());
auto map = [&](const size_t& index) -> auto& { return values_original[index]; };
auto values_mapped = xt::vectorize(map)(indexes);
for (size_t i = 0; i < values_original.size(); ++i) {
EXPECT_TRUE(&(values_mapped[i]) == &(values_original[i]));
}The reason is in this function:
xtensor/include/xtensor/core/xfunction.hpp
Lines 1108 to 1118 in 5caa64d
Here, the lambda needs to have a return type reference instead of returning by value.
The same problem occurs in every use case of std::apply in xfunction.hpp.
Reacted by Sylvain Corlay
Activity
JohanMabille commentedon May 6, 2026
Wow good catch! Unbelievable that we haven't catched it earlier!
Fixed lambda return type used in xfunxtion (xtensor-stack#2913)