------- Comment #2 from jarausch at igpm dot rwth-aachen dot de 2009-10-22
10:35 -------
(In reply to comment #1)
> I don't think this is misparsing this at all. This is one place in the C++
> standard that says it should be parsed as a function declaration rather than a
> variable declaration to resolve an ambiguous between those two.
>
There are different opinions about that.
The current Comeau compiler does accept the code.
Here an answer James Kanze on the news group comp.lang.c++
First, there is absolutely no way that proj can be interpreted
as a function declaration; the string literal prevents that,
regardless of anything else. Second, if "space" is the
name of a type (as it is in your code), »space(V[i])« is a
function declaration in any context that allows function
declarations. The only contexts which allow declarations
other than at the statement level, however, is as part of other
declarations; the only context in which a function declaration
can be followed by a comma is as a parameter in another function
declaration. Since in this case, the string literal means that
this statement cannot be a function declaration, »space(V[i])«
cannot be a parameter declaration, and thus, cannot be a
function declaration. There's no ambiguity. (This is a
difficult parse, however, since the interpretation here depends
on context. In something like:
form proj( space(V[i]) );
»space(V[i])« is a function declaration, and the entire
statement is a function declaration, because there is nothing
which makes it illegal as a function declaration.)
I do remember earlier versions of g++ (2.95.2?) having problems
with this; they didn't consider context to the right of the
expression when making the decision, so something like:
form proj( space(V[i]), "abc" );
would fail to compile, treating »space(V[i])« as a function
declaration, whereas:
form proj( "abc", space(V[i]) );
worked, since the preceding string literal had removed the
ambiguity of the context. Later versions of g++ fixed this. It
sounds to me like they've reintroduced the bug, and that someone
has decided (on what grounds, I don't know), that it's not a
bug, but a feature.
This is probably a shorter test case:
struct A { A(int, char const*); };
int main() {
int i = 0, *b = &i;
A a(int(b[i]), "hello");
}
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41786
