On Wednesday, 29 May 2013 at 04:15:52 UTC, Walter Bright wrote:
On 5/28/2013 7:40 PM, Jesse Phillips wrote:
On Monday, 27 May 2013 at 07:53:05 UTC, Walter Bright wrote:
In D, right now (and especially with the beta) you can use
the NotNull template.
Where is this NotNull template? If it was in Phobos I would
expect
http://dlang.org/phobos/std_typecons.html
It's not in Phobos yet:
struct NotNull(T) {
T p;
alias p this;
this(T p) {
assert(p != null, "pointer is null");
this.p = p;
}
@disable this();
NotNull opAssign(T p) {
assert(p != null, "assigning null to NotNull");
this.p = p;
return this;
}
}
Doing this would help move some of that to compile time:
struct NotNull(T) {
T ptr;
alias ptr this;
this(U : T)(U p) {
assert(p !is null, "pointer is null");
this.ptr = p;
}
this(U : typeof(null))(U p) {
static assert(false, "pointer is null");
}
NotNull opAssign(U : T)(U p) {
assert(p !is null, "assigning null to NotNull");
this.ptr = p;
return this;
}
NotNull opAssign(U : typeof(null))(U p) {
static assert(false, "assigning null to NotNull");
}
}
Although I think it would be better still if it didn't
automatically convert from T as that removes half the benefit of
a statically checked NotNull.
One thing you could do is overload the OR operator for "T ||
NotNull!T" as it is perfectly safe to construct a NotNull!T from
that. Plus with shortcut evaluation there is no performance cost.
As a last resort there should be a runtime check available such
as assertNotNull(T) which does the conversion.
