On Thursday, 29 November 2012 at 02:34:11 UTC, Walter Bright
wrote:
For discussion:
Cyclical Imports
Problem:
---- a.d ----
module a;
import b;
static this () { ... }
---- b.d ----
module b;
import a;
static this() { ... }
-------------
Static constructors for a module are only run after static
constructors
for all its imports are run. Circular imports, such as the
above, are
detected at run time and the program is aborted.
This can in general be solved by moving the static
constructor(s) into
a third module, c.d, which does not import a or b. But, people
find this
to be unnatural.
Proposed Solution:
Add a pragma,
pragma(cyclic_imports);
This can appear anywhere in a module, and applies globally to
that module.
It means that static constructors from imports that are not
part of the cycle
are run first, and that the static constructor for this module
may be run before
the static constructors of other modules that are part of the
cycle.
If any static constructors in such a module with the pragma have
the @safe attribute, that is a compile time error.
While more complex, would it be possible to declare which
imported modules can be constructed after the current one? That
allows catching any other unintended cyclic imports. For example:
static this {
pragma(cyclic_import, b);
// code that does not depend on
// static constructor(s) in module b
}
