C++ auto& vs auto

Question

When creating local variables, is it correct to use (const) auto& or auto?

e.g.:

SomeClass object;
const auto result =          


        

Answer 1

When creating local variables, is it correct to use (const) auto& or auto?

Yes. The auto is nothing more than a compiler-deduced type, so use references where you would normally use references, and local (automatic) copies where you would normally use local copies. Whether or not to use a reference is independent of type deduction.

Where SomeMethod() returns a non-primitive value - maybe another user-defined type. My understanding is that const auto& result is correct since the result returned by SomeMethod() would call the copy constructor for the returned type. Please correct me if I am wrong.

Legal? Yes, with the const. Best practice? Probably not, no. At least, not with C++11. Especially not, if the value returned from SomeMethod() is already a temporary. You'll want to learn about C++11 move semantics, copy elision, and return value optimization: https://juanchopanzacpp.wordpress.com/2014/05/11/want-speed-dont-always-pass-by-value/

http://www.informit.com/guides/content.aspx?g=cplusplus&seqNum=199

https://isocpp.org/wiki/faq/ctors#return-by-value-optimization

What about for primitive types? I assume const auto sum = 1 + 2; is correct.

Yes, this is fine.

Does this also apply to range based for loops?

for(const auto& object : objects)

Yes, this is also fine. I write this sort of code at work all the time.