Re: Is there a way to disable copying of an alias this'd member? - trying to make a NotNull type
On Friday, 24 May 2019 at 12:03:08 UTC, Simen Kjærås wrote:
On Friday, 24 May 2019 at 11:40:20 UTC, aliak wrote:
It's ref so that you can do this for e.g.
class C { int i; }
auto a = notNull!C;
a.i = 3;
That's a valid concern for a struct, but classes are already
reference types, so you're only adding a new layer of ref-ness.
The above will work great with a non-ref alias this.
--
Simen
Ah true. Yes I guess I can do this for ref types indeed. And
maybe I can just constrain it to classes, interfaces and pointers
樂
Cheers,
- Ali
Re: Is there a way to disable copying of an alias this'd member? - trying to make a NotNull type
On Friday, 24 May 2019 at 11:40:20 UTC, aliak wrote:
It's ref so that you can do this for e.g.
class C { int i; }
auto a = notNull!C;
a.i = 3;
That's a valid concern for a struct, but classes are already
reference types, so you're only adding a new layer of ref-ness.
The above will work great with a non-ref alias this.
--
Simen
Re: Is there a way to disable copying of an alias this'd member? - trying to make a NotNull type
On Friday, 24 May 2019 at 10:40:01 UTC, Simen Kjærås wrote:
On Friday, 24 May 2019 at 10:16:50 UTC, aliak wrote:
Basically, I want this to fail:
auto notNull(T, Args...)(Args args) {
return NotNull!T(new T(args));
}
struct NotNull(T) {
private T _value;
@property ref inout(T) value() inout { return this._value; }
alias value this;
//disable opAssign to null as well
}
class C {}
void func(ref C t) {
t = null;
}
auto a = notNull!C;
func(a); // i want a compile error here
Any ideas that don't involve disabling copying or making the
property non-ref?
Pretty sure that can't be done. On the other hand, why is the
property ref if you're explicitly not going to use its
ref-ness? Alternatively, can you show me how you use its
ref-ness?
It's ref so that you can do this for e.g.
class C { int i; }
auto a = notNull!C;
a.i = 3;
I guess maybe there's a way to go about supporting that kinda
thing with opDispatch. But I've tried doing that in the optional
type [0] and it's rather painful to get right, and trickier to
make @safe as well.
And just for completeness, you are aware that alias this takes
an overload set, so that this works?
struct NotNull(T) {
private T _value;
@property inout(T) value() inout { return _value; }
@property void value(T val) { _value = val; } // new
alias value this;
// disable opAssign to null as well
}
class C {}
void func(ref C t) { t = null; }
unittest {
NotNull n;
n = new C(); // Look ma, I'm assigning without ref!
func(n); // Does not compile - value() doesn't return by
ref
}
--
Simen
Si si. I is aware. I've disabled opAssign to T actually (i think
i have at least). And I only allow assigning to another NotNull
else there's no way to guarantee that the NotNull stays non null.
It looks like I'm going to have to sacrifice being able to
manipulate member variables of the type the NotNull is wrapping,
or give up on the guarantee of the inner value not being null.
[0] https://code.dlang.org/packages/optional
Re: Is there a way to disable copying of an alias this'd member? - trying to make a NotNull type
On Friday, 24 May 2019 at 10:40:01 UTC, Simen Kjærås wrote: NotNull n; Typo. Should be NotNull!C n; -- Simen
Re: Is there a way to disable copying of an alias this'd member? - trying to make a NotNull type
On Friday, 24 May 2019 at 10:16:50 UTC, aliak wrote:
Basically, I want this to fail:
auto notNull(T, Args...)(Args args) {
return NotNull!T(new T(args));
}
struct NotNull(T) {
private T _value;
@property ref inout(T) value() inout { return this._value; }
alias value this;
//disable opAssign to null as well
}
class C {}
void func(ref C t) {
t = null;
}
auto a = notNull!C;
func(a); // i want a compile error here
Any ideas that don't involve disabling copying or making the
property non-ref?
Pretty sure that can't be done. On the other hand, why is the
property ref if you're explicitly not going to use its ref-ness?
Alternatively, can you show me how you use its ref-ness?
And just for completeness, you are aware that alias this takes an
overload set, so that this works?
struct NotNull(T) {
private T _value;
@property inout(T) value() inout { return _value; }
@property void value(T val) { _value = val; } // new
alias value this;
// disable opAssign to null as well
}
class C {}
void func(ref C t) { t = null; }
unittest {
NotNull n;
n = new C(); // Look ma, I'm assigning without ref!
func(n); // Does not compile - value() doesn't return by
ref
}
--
Simen
