带有默认参数构造的noexcept说明符

Question

Take the following example code:

void test(const Item& item = Item()) {
   ...
}

Assume that, once item has been passed to the function, this cannot throw.

The question is: the function should be marked noexcept or noexcept(noexcept(Item())) ?

IHMO, the former should be ok, but I am not sure. A quotation from the standard would be very appreciated!

Answer 1

Default arguments are shortcut notations for the caller of function. So, when the function executes, the construction is already complete.

Thus, noexcept should be sufficient.

In the standard [dcl.fct.default] states:

If an initializer-clause is specified in a parameter-declaration this initializer-clause is used as a default argument. Default arguments will be used in calls where trailing arguments are missing.

Example: the declaration void point(int = 3, int = 4); declares a function that can be called with zero, one, or two arguments of type int. It can be called in any of these ways: point(1,2); point(1); point(); The last two calls are equivalent to point(1,4) and point(3,4) , respectively.

Also there is a note (in [intro.execution] Program execution):

Subexpressions involved in evaluating default arguments (8.3.6) are considered to be created in the expression that calls the function, not the expression that defines the default argument