What type is decltype?

The decltype type specifier yields the type of a specified expression. The decltype type specifier, together with the auto keyword, is useful primarily to developers who write template libraries. Use auto and decltype to declare a template function whose return type depends on the types of its template arguments.

What does decltype mean in C++?

In the C++ programming language, decltype is a keyword used to query the type of an expression. In general, the deduced type matches the type of the object or function exactly as declared in the source code. Like the sizeof operator, decltype ‘s operand is not evaluated.

What is the difference between decltype and auto?

‘auto’ lets you declare a variable with a particular type whereas decltype lets you extract the type from the variable so decltype is sort of an operator that evaluates the type of passed expression.

What does decltype return?

decltype returns If what we pass to decltype is the name of a variable (e.g. decltype(x) above) or function or denotes a member of an object ( decltype x.i ), then the result is the type of whatever this refers to. As the example of decltype(y) above shows, this includes reference, const and volatile specifiers.

What does decltype stand for?

declared type
Decltype stands for declared type of an entity or the type of an expression. It lets you extract the type from the variable so decltype is sort of an operator that evaluates the type of passed expression.

Is runtime a decltype?

decltype is a compile time evaluation (like sizeof ), and so can only use the static type.

What does decltype auto do?

decltype(auto) is primarily useful for deducing the return type of forwarding functions and similar wrappers, where you want the type to exactly “track” some expression you’re invoking.

Where is decltype used?

1. You should use decltype when you want a new variable with precisely the same type as the original variable.
2. You should use auto when you want to assign the value of some expression to a new variable and you want or need its type to be deduced.

What are Lvalues and Rvalues?

An lvalue refers to an object that persists beyond a single expression. An rvalue is a temporary value that does not persist beyond the expression that uses it.

Is decltype evaluated at compile time?

Should I use C++ Auto?

If the context makes it clear what type it is, or at least how it should be used (in case of standard container iterator) or the knowledge of the actual type is not even needed (such as in expression templates), then auto should be used, and if the context doesn’t make it clear and isn’t very common (such as the second …

Is runtime a Decltype?

https://www.youtube.com/watch?v=j6FG28KlgMI