On 01/31/2013 08:34 PM, Dmitry Olshansky wrote:
31-Jan-2013 23:32, Maxim Fomin пишет:
On Thursday, 31 January 2013 at 19:17:56 UTC, Dmitry Olshansky wrote:
31-Jan-2013 19:21, Andrei Alexandrescu пишет:
On 1/31/13 10:18 AM, Steven Schveighoffer wrote:
On Thu, 31 Jan 2013 10:12:53 -0500, Andrei Alexandrescu
As far as I can tell classes have the same problem.
Nope.
void foo(someclass aa, int x, int y)
{
aa[x] = y;
}
void main()
{
someclass aa;
foo(aa, 1, 2); // segfault
...
}
We could easily arrange things to segfault just the same with a
struct-based implementation.
Structs are quite borked in this regard e.g. without extra efforts the
following:
somclass aa = someclass();
foor(aa, 1, 2); // segfault, surprize someclass() is someclass.init
The current workaround I find the most sensible is:
- @disable this();
- make all constructors private
- define opCall and forward it to private constructors. 0-arg versions
have to pass dummy and/or default values to get struct constructed
- automate this boilerplate until something in language is fixed? :)
The advantage is that the following is illegal:
someclass aa;
and the following works as expected:
auto aa = someclass(); //create empty container damn it!
If desired default struct value is constant for all instances of that
struct, there is another workaround by changing init values:
-------------------
import std.stdio;
class A { int x = 5; }
struct S { int x = 5; A a; }
void main()
{
S s; // defaults to preallocated a, a is not null
assert(S.x is 100 && s.a !is null && s.a.x is 100);
}
This is fine except that it doesn't solve the problem of:
Container a = Container(); //should be empty container, not illegal
null-container
Just use a payload struct and check whether that is null before every
operation.
Basically @dsiable this() is optional, but I like to help user avoid
bugs.
import runtime;
mixin(declareExternInitZPointer!S);
static this()
{
A a = new A;
a.x = 100;
S s = S(100, a);
rtSetDefaultHeapInitializer(s);
rtSetDefaultStackInitializer(s, mixin(passExternInitZPointer!S));
}
----------------------
Where runtime module is http://dpaste.dzfl.pl/40b59a5d
This does not fully replace default ctor, since all instances of S are
affected.
