• Shachar Shemesh (39/39) Apr 12 2018 I'm trying to build a wrapper that will allow you to copy structs that
• Uknown (8/14) Apr 12 2018 The problem seems to be that cast is happening at compile time,
• Shachar Shemesh (10/25) Apr 12 2018 struct Disabled {
• Eduard Staniloiu (5/28) Apr 15 2018 Since `T` has the postblit disabled, I'm guessing the ctor should

Shachar Shemesh <shachar weka.io> writes:

I'm trying to build a wrapper that will allow you to copy structs that 
have members that disabled copying. The idea is that copying these 
members will revert them to init.

This is what I have so far:

struct NoCopy(T) {
     static assert( !hasElaborateDestructor!T, "NoCopy does not support 
type " ~ T.stringof ~ " with elaborate destructor" );

private:
     ubyte[T.sizeof] __bytes;

public:
     this(T val) {
         __bytes[] = (cast(const ubyte *)&val)[0..T.sizeof][];
     }

      property ref inout(T) value() inout nothrow  trusted  nogc {
         return *cast(inout T*)__bytes.ptr;
     }

     this(this) {
         value = T.init;
     }

     void opAssign(NoCopy rhs) {
         value = T.init;
     }

     void opAssign(T rhs) {
         value = move(rhs);
     }

     alias this value;
}

I'm having problems with setting the initial value for the byte array. 
The technique I use in "value" does not work for initialization:

test.d(19): Error: cannot convert &S to const(ubyte*) at compile time

At first, I said "fine, the user will do it". That doesn't work, 
however. It doesn't matter who tries to do it, I cannot get the byte 
value of the type at compile time.

I tried using a union, but that, too, doesn't work.

I understand why the restriction is in place. What I'm wondering is 
whether there is any other solution, either to the init problem or to 
the overriding disable problem.

Thank you,
Shachar

Uknown <sireeshkodali1 gmail.com> writes:

On Thursday, 12 April 2018 at 12:16:53 UTC, Shachar Shemesh wrote:
 [...]
 test.d(19): Error: cannot convert &S to const(ubyte*) at 
 compile time
 [...]
 Thank you,
 Shachar

The problem seems to be that cast is happening at compile time, 
as opposed to run time, as you might have already figured out. Do 
you need to really do this cast at compile time? I tried running 
the snippet you gave here: https://run.dlang.io/is/im19nL

Is this how you intend for it to be used? Then there's no need 
for compile time casts. If not, could you give an example of how 
`NoCopy` would be used?

Shachar Shemesh <shachar weka.io> writes:

On 12/04/18 18:42, Uknown wrote:
 On Thursday, 12 April 2018 at 12:16:53 UTC, Shachar Shemesh wrote:
 [...]
 test.d(19): Error: cannot convert &S to const(ubyte*) at compile time
 [...]
 Thank you,
 Shachar

 
 The problem seems to be that cast is happening at compile time, as 
 opposed to run time, as you might have already figured out. Do you need 
 to really do this cast at compile time? I tried running the snippet you 
 gave here: https://run.dlang.io/is/im19nL
 
 Is this how you intend for it to be used? Then there's no need for 
 compile time casts. If not, could you give an example of how `NoCopy` 
 would be used?

struct Disabled {
   int i = 17;

    disable this(this);
}

struct Container {
   NoCopy!Disabled disabled;
}

Any instance you create of "Container" will have i initialized to 0 by 
default.

Eduard Staniloiu <edi33416 gmail.com> writes:

On Thursday, 12 April 2018 at 17:09:22 UTC, Shachar Shemesh wrote:
 On 12/04/18 18:42, Uknown wrote:
 On Thursday, 12 April 2018 at 12:16:53 UTC, Shachar Shemesh 
 wrote:
 [...]

 
 The problem seems to be that cast is happening at compile 
 time, as opposed to run time, as you might have already 
 figured out. Do you need to really do this cast at compile 
 time? I tried running the snippet you gave here: 
 https://run.dlang.io/is/im19nL
 
 Is this how you intend for it to be used? Then there's no need 
 for compile time casts. If not, could you give an example of 
 how `NoCopy` would be used?

 struct Disabled {
   int i = 17;

    disable this(this);
 }

 struct Container {
   NoCopy!Disabled disabled;
 }

 Any instance you create of "Container" will have i initialized 
 to 0 by default.

Since `T` has the postblit disabled, I'm guessing the ctor should 
take a `ref T`.

Since `T` has the postblit disabled, I'm guessing the ctor should 
take a `ref T`.