digitalmars.D - Static initialization of pointers
- Adrian Matoga (18/41) Jul 27 What is the rationale of making this implementation defined?
The D language specification under "Global and static initializers" , says the following:The Initializer for a global or static variable must be evaluatable at compile time. Whether some pointers can be initialized with the addresses of other functions or data is implementation defined. Runtime initialization can be done with static constructors.What is the rationale of making this implementation defined? What's the range of possible behaviors? Are there any circumstances in which a pointer can't be initialized with an address of a function or data? If so, couldn't a subset of cases have an explicitly defined, portable behavior? As far as I've tested this, DMD, GDC and LDC can handle static initialization of pointers to functions or data (except that LDC fails if function pointer(s) are obtained via __traits(getUnitTests, module_name)), even across separately compiled modules, which is consistent with a similar feature of C and C++. IIUC, the C standard always allows such initialization. In 6.6 Constant expressions, N1570  says:7 More latitude is permitted for constant expressions in initializers. Such a constant expression shall be, or evaluate to, one of the following: — an arithmetic constant expression, — a null pointer constant, — an address constant, or — an address constant for a complete object type plus or minus an integer constant expression.and9 An address constant is a null pointer, a pointer to an lvalue designating an object of static storage duration, or a pointer to a function designator; it shall be created explicitly using the unary & operator or an integer constant cast to pointer type, or implicitly by the use of an expression of array or function type. The array-subscript  and member-access . and -> operators, the address & and indirection * unary operators, and pointer casts may be used in the creation of an address constant, but the value of an object shall not be accessed by use of these operators. https://dlang.org/spec/declaration.html#global_static_init  http://iso-9899.info/n1570.html