CWG2711 [except.throw] It is not specified what the exception object is copy-initialized from

[t3nsor]

Full name of submitter: Brian Bi

Reference (section label): [except.throw]

Issue description: As pointed out by user 0x5f3759df on Stack Overflow, the normative wording in [expr.throw] and [except.throw] respectively specify the type of the exception object and the fact that the exception object is copy-initialized, but do not appear to specify that the exception object is copy-initialized from the assignment-expression operand.

Suggested resolution: Edit [except.throw]/3:

Throwing an exceptionA throw-expression ([expr.throw]) with an operand copy-initializes (9.4, 11.4.5.3) a temporary object, called the exception object, from its operand. If the type of the exception object would be an incomplete type, an abstract class type (11.7.4), or a pointer to an incomplete type other than cv void the program is ill-formed.

[jensmaurer]

This isn't good; there are situations in the language where we throw exceptions without a throw-expression (for example, a failed dynamic cast or a failed typeid).

We still want to initialize an exception object in these cases.

[jensmaurer]

CWG2711

[t3nsor]

Good catch. Thanks for fixing the wording.