How much is too much with C++11 auto keyword?

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I've been using the new auto keyword available in the C++11 standard for complicated templated types which is what I believe it was designed for. But I'm also using it for things like:

auto foo = std::make_shared<Foo>();

And more skeptically for:

auto foo = bla(); // where bla() return a shared_ptr<Foo>

I haven't seen much discussion on this topic. It seems that auto could be overused since a type is often a form of documentation and sanity checks. Where do you draw the line in using auto and what are the recommended use cases for this new feature?

To clarify: I'm not asking for a philosophical opinion; I'm asking for the intended use of this keyword by the standard committee, possibly with comments on how that intended use is realized in practice.

auto type-inference c++11 c++ types
15 Answers

What auto does?

It tells compiler to infer(determine) the variable's data type based on its initialized value. It uses type deduction.

Where should auto be used?

  • When you are not interested in knowing the type of variable and just want to use it.

  • When you want to avoid incredibly long and ugly typenames.

  • When you are not sure of the type himself.

  • When you do not want to see uninitialized variables in your code i.e. auto forces you to initialize a variable hence you can’t forget doing that.

When it should not be used or Cons of auto

  • Referring to its functionality, auto may deduce type incorrectly, One such case is
 std::vector<bool> vec(10, 0);

 auto x = vec[2];

 bool y = vec[2];

 std::cout << typeid(x).name() << "\n";

 std::cout << typeid(y).name() << "\n";

The output on G++ 10.2 is surprising:

St14_Bit_reference

b
  • It should not be used if you want to make your code readable & Understandable for other people. It hides the data type visibility from the reader.
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