structured-bindings

问题 Functional languages with pattern matching (sometimes?) have the possibility to ignore some bound values, but with C++17 structured bindings there seem to be no way to do that (std::ignore with structured bindings?). The advice is to use a dummy name, but then we'll get warnings about unused variables. With the latest heads of both clang and gcc, this does the expected thing, which is nice and useful, [[maybe_unused]] auto x =4 ; // fine, no warning [[maybe_unused]] auto [a,dummyb,dummyc] =

问题 With the following code, I get a compile error C2065 'a': undeclared identifier (using visual studio 2017): [] { auto [a, b] = [] {return std::make_tuple(1, 2); }(); auto r = [&] {return a; }(); //error C2065 }(); However, the following code compiles: [] { int a, b; std::tie(a, b) = [] {return std::make_tuple(1, 2); }(); auto r = [&] {return a; }(); }(); I thought that the two samples were equivalent. Is it a compiler bug or am I missing something ? 回答1: Core issue 2313 changed the standard

问题 Yesterday I\'ve seen an interesting question here on SO about structured binding. We can sum up it as it follows. Consider the example code below: #include <tuple> #include <type_traits> int main() { auto tup = std::make_tuple(1, 2); auto & [ a, b ] = tup; // the following line won\'t compile for a isn\'t a reference // static_assert(std::is_reference_v<decltype(a)>); } In this case decltype(a) is int (probably) because of this bullet (working draft): if e is an unparenthesized id-expression