[Issue 9112] New: Uniform default construction

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=9112

           Summary: Uniform default construction
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: k.hara.pg at gmail.com


--- Comment #0 from Kenji Hara <k.hara.pg at gmail.com> 2012-12-03 20:06:08 PST ---
Related: http://d.puremagic.com/issues/show_bug.cgi?id=8752

Built-in .init property is useful, but it is sometimes unsafe, and many people
might confuse the default initializer and construction.

- Default initializer represents pre-constructing object state.
  Users can access to it by using built-in `.init` property.

- Default construction is a default operation which constructing an object
  completely.
  * For built-in types (int, double, pointers, arrays) and class types,
    default construction does nothing. Because, after initializing by
    default initializer, the object is already completely constructed.
  * For struct types, it is same in basic. After initialized by S.init,
    the object is completely constructed. Except:
    + If S is a nested struct, default construction should fill
      its frame pointer. So default construction is valid only in
     the function where S is defined.
    + If S is a struct which has `@disable this();`, default construction
      is disabled explicitly. So default construction is never occur.
      Instead, users should call explicitly defined user-defined
      constructor which has arguments.

Well, for struct types, default construction has an explicit syntax S().
But, built-in types does not have that. It is inconsistent.

So I'd like to propose new syntax to reduce such concept confusion.

int n = int();    // same as int.init
int n = int(10);  // same as cast(int)10;

>From the meta-programming view, we can represent default construction of value
types by T().

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