Re: Throw a reference and assignment-expression in throw-expression

=?UTF-8?B?RGFuaWVsIEtyw7xnbGVy?= <>
Thu, 27 Nov 2014 13:35:07 CST
Am 26.11.2014 um 20:15 schrieb Adam Badura:

I was browsing through the Standard (N3337 in this case) to refresh my
knowledge about exceptions and throwing in particular. And there is
something that I???m unable to understand. In 15.1$3 there is:


Now the question is what about references? Consider code (lets skip any
???design issues???):

int& get_object() {
    static int var = 0;
    return var;

void f() {
    throw get_object();

What gets thrown by f() is an object of int type that has nothing to do
with get_object()???s var except for the initial value at the throw moment.

While according to how I understand the cited fragment the static type of
throw operand is here int& rather than int. So the temporary exception
object should be int& rather than int. And thus should be a reference to
actual get_object()???s var rather than a copy of it.

No, that won't happen. During the analysis of an expression by the
compiler a very fundamental part of what happens in the beginning is
specified by Clause 5 p5:

"If an expression initially has the type ???reference to T??? (8.3.2,
8.5.3), the type is adjusted to T prior to any further analysis. The
expression designates the object or function denoted by the reference,
and the expression is an lvalue or an xvalue, depending on the expression."

So the fact that get_object() returns an lvalue reference to int does
not cause the expression to have type "int&", the expression


has type int and is an lvalue.

It is obvious that my understanding of the cited fragment is just wrong.
But why? Is there something else that I don???t see? Or did not follow
references thoroughly enough?

See above.

HTH & Greetings from Bremen,

Daniel Kr??gler

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