I think that one should use the auto
keyword whenever it’s hard to say how to write the type at first sight, but the type of the right hand side of an expression is obvious. For example, using:
my_multi_type::nth_index<2>::type::key_type::composite_key_type::
key_extractor_tuple::tail_type::head_type::result_type
to get the composite key type in boost::multi_index
, even though you know that it is int
. You can’t just write int
because it could be changed in the future. I would write auto
in this case.
So if the auto
keyword improves readability in a particular case then use it. You can write auto
when it is obvious to the reader what type auto
represents.
Here are some examples:
auto foo = std::make_shared<Foo>(); // obvious
auto foo = bla(); // unclear. don't know which type `foo` has
const size_t max_size = 100;
for ( auto x = max_size; x > 0; --x ) // unclear. could lead to the errors
// since max_size is unsigned
std::vector<some_class> v;
for ( auto it = v.begin(); it != v.end(); ++it )
// ok, since I know that `it` has an iterator type
// (don't really care which one in this context)