I think it's not OK to accept x3 assignment and refuse the a2 assignment:


struct Foo {
    immutable(char)[4] bar;
}
Foo x1 = { "AA" };            // No error.
immutable(char)[4] a1 = "AA"; // No error.
void main() {
    Foo x2 = { "AA" };        // No error.
    Foo x3 = Foo("AA");       // No error.
    immutable(char)[4] a2 = "AA"; // Error: lengths don't match
                                  // for array copy, 4 = 2
}


Kenji Hara answers:
http://forum.dlang.org/post/akeivrewkkhjuapbngel@forum.dlang.org

> This is known static array initializing inconsistency between
> DeclDefs scope and statement scope. I think it is a bug.


See also, where I say that I think all of those five cases should be reported as bugs:
http://d.puremagic.com/issues/show_bug.cgi?id=3849