|  | Is decltype(vector())::iterator valid? If not, should i | | |
| | | Chris Fairles |  |
|  Posted: Sat Aug 30, 2008 3:08 pm Post subject: Is decltype(vector())::iterator valid? If not, should i |  |
Take the following snip:
#include <vector>
int main()
{
decltype(vector<int>())::iterator i;
}
Currently gcc 4.4.0 mainline issue a diagnostic: expected initializer
before 'i'.
So, looking at n2723, "decltype (expression)" is a simple-type-
specifier and am I correct in saying that this is the reason why the
snip is ill-formed (i.e.the scope resolution operator can't be applied
to a simple-type-specifier)?
You can make the snip work by re-defining decltype using a macro:
#include <vector>
#define decltype(x) ::std::identity<decltype(x)>::type
int main()
{
decltype(vector<int>())::iterator i;
}
and voila, it now works as expected. So why wouldn't everyone just
define decltype like that and be able to apply the scope resolution
operator to decltype()'s?
Chris
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| | | Triple-DES | |
| | Posted: Sun Aug 31, 2008 8:58 am Post subject: Re: Is decltype(vector())::iterator valid? If not, shou | |
On 30 Aug, 17:08, Chris Fairles <chris.fair...@gmail.com> wrote:
| Quote: | Take the following snip:
#include <vector
int main()
{
decltype(vector<int>())::iterator i;
}
Currently gcc 4.4.0 mainline issue a diagnostic: expected initializer
before 'i'.
So, looking at n2723, "decltype (expression)" is a simple-type-
specifier and am I correct in saying that this is the reason why the
snip is ill-formed (i.e.the scope resolution operator can't be applied
to a simple-type-specifier)?
|
I asked the very same question some time ago.
According to Daveed Vandevoorde: "The grammar doesn't allow a decltype
construct to appear as a
qualifier. It has to be a namespace-name, a class-name, a typedef-
name, or an enum-name"
DP
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