Access auto parameter's type within lambda

Question

I'm using a lambda function for boilerplate code:

auto import = [&](auto & value){
   // Do some stuff
};

As value is in fact a std::vector, I need to access its value_type static member to call a template function on one of its element.

I tried use of decltype without success :

auto import = [&](auto & value){
   decltype(value)::value_type v;
};

Is there any way to do so ?

`use of 'auto' in lambda parameter declaration only available with c++14`... please update your question tag — NutCracker, Apr 23 '20 at 10:11

songyuanyao · Accepted Answer · 2020-04-23T10:28:32.460

3

The type of value is an lvalue-reference, you can't get the member type from it and have to remove the reference part, e.g

typename std::decay_t<decltype(value)>::value_type v;

edited Apr 23 '20 at 10:28

answered Apr 23 '20 at 10:11

songyuanyao

1

`typename` is also needed. – HolyBlackCat Apr 23 '20 at 10:13
2

@HolyBlackCat Yes, so we need to combine the two answers to get the correct solution.. – songyuanyao Apr 23 '20 at 10:15
Yes, typename std::decay_t::value_type works perfectly. Thanks. – etham Apr 23 '20 at 10:19

1 Answers1