• Kagamin (7/7) Feb 03 2018 ---
• Steven Schveighoffer (8/16) Feb 05 2018 Superficially, it looks like it should work, given the previous 2 lines.
• Kagamin (6/7) Feb 06 2018 Maybe for least surprise. The error message almost convinced me
• Steven Schveighoffer (23/29) Feb 06 2018 Honestly, I don't know why it's not working. But maybe there is a reason...
• Temtaime (2/9) Feb 06 2018 Fill a bugreport.

Kagamin <spam here.lot> writes:

---
interface A{}

void* a=cast(void*)5;
A b=cast(A)a; //ok
A c=cast(A)cast(void*)5; //error
---
Last line gives Error: cannot cast `void*` to `A`. Is it intended?

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 2/3/18 12:37 PM, Kagamin wrote:
 ---
 interface A{}
 
 void* a=cast(void*)5;
 A b=cast(A)a; //ok
 A c=cast(A)cast(void*)5; //error
 ---
 Last line gives Error: cannot cast `void*` to `A`. Is it intended?

Superficially, it looks like it should work, given the previous 2 lines.

But I don't know what the compiler does to convince itself your code is 
wrong when you do it all in one expression.

Is there a more pragmatic use case why this should be possible? It would 
help give motivation for fixing the problem. Clearly, `5` isn't going to 
be a valid interface pointer.

-Steve

Kagamin <spam here.lot> writes:

On Monday, 5 February 2018 at 15:33:02 UTC, Steven Schveighoffer 
wrote:
 Is there a more pragmatic use case why this should be possible?

Maybe for least surprise. The error message almost convinced me 
that such cast is impossible, only because of my memory that this 
cast used to be possible kept me trying. Is 5 not good because 
it's not big enough?

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 2/6/18 3:29 AM, Kagamin wrote:
 On Monday, 5 February 2018 at 15:33:02 UTC, Steven Schveighoffer wrote:
 Is there a more pragmatic use case why this should be possible?

 
 Maybe for least surprise. The error message almost convinced me that 
 such cast is impossible, only because of my memory that this cast used 
 to be possible kept me trying. Is 5 not good because it's not big enough?

Honestly, I don't know why it's not working. But maybe there is a reason 
(i.e. it's not a bug and was done on purpose).

All I meant is that, if you have a more practical correct reason for 
casting an integer literal to an interface, then we can show that it's 
worth worrying about.

By illustration of what I'm talking about, D complains about this:

int * foo()
{
    int x;
    return &x;
}

But not this:

int * bar()
{
    int x;
    int *p = &x;
    return p;
}

Complaining about not being able to cast 5 directly to an interface, 
when you can do it in 2 statements, may be like complaining that bar 
compiles, why not foo?

-Steve

Temtaime <temtaime gmail.com> writes:

On Tuesday, 6 February 2018 at 08:29:05 UTC, Kagamin wrote:
 On Monday, 5 February 2018 at 15:33:02 UTC, Steven 
 Schveighoffer wrote:
 Is there a more pragmatic use case why this should be possible?

 Maybe for least surprise. The error message almost convinced me 
 that such cast is impossible, only because of my memory that 
 this cast used to be possible kept me trying. Is 5 not good 
 because it's not big enough?

Fill a bugreport.