Explicit Type Conversion and Multiple Simple Type Specifiers
- by James McNellis
To value initialize an object of type T, one would do something along the lines of one of the following:
T x = T();
T x((T()));
My question concerns types specified by a combination of simple type specifiers, e.g., unsigned int:
unsigned int x = unsigned int();
unsigned int x((unsigned int()));
Visual C++ 2008 and Intel C++ Compiler 11.1 accept both of these without warnings; Comeau 4.3.10.1b2 and g++ 3.4.5 (which is, admittedly, not particularly recent) do not.
According to the C++ standard (C++03 5.2.3/2, expr.type.conv):
The expression T(), where T is a simple-type-specifier (7.1.5.2) for a non-array complete object type or the (possibly cv-qualified) void type, creates an rvalue of the specified type, which is value-initialized
7.1.5.2 says, "the simple type specifiers are," and follows with a list that includes unsigned and int.
Therefore, given that in 5.2.3/2, "simple-type-specifier" is singular, and unsigned and int are two type specifiers, are the examples above that use unsigned int invalid? (and, if so, the followup is, is it incorrect for Microsoft and Intel to support said expressions?)
This question is more out of curiosity than anything else; for all of the types specified by a combination of multiple simple type specifiers, value initialization is equivalent to zero initialization. (This question was prompted by comments in response to this answer to a question about initialization).
