• John Colvin (11/11) Jan 09 2015 struct S
• anonymous (4/15) Jan 09 2015 You'd expect `cast(void*)s == s.p`? That doesn't work for any
• John Colvin (4/22) Jan 09 2015 I was expecting it to work regardless of the type of p. I have an
• Steven Schveighoffer (6/28) Jan 09 2015 This is actually a compiler bug! I will check to make sure it's not
• John Colvin (4/19) Jan 13 2015 So it is! The same happens with e.g. casting void* to string.
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (10/21) Jan 09 2015 I know two options:

"John Colvin" <john.loughran.colvin gmail.com> writes:

struct S
{
     void* p;
}

void main()
{
     S s;
     auto a = cast(void*)s; //Error: e2ir: cannot cast s of type S 
to type void*
}

Is there are a good reason for this being disallowed?

"anonymous" <anonymous example.com> writes:

On Friday, 9 January 2015 at 18:25:42 UTC, John Colvin wrote:
 struct S
 {
     void* p;
 }

 void main()
 {
     S s;
     auto a = cast(void*)s; //Error: e2ir: cannot cast s of type 
 S to type void*
 }

 Is there are a good reason for this being disallowed?

You'd expect `cast(void*)s == s.p`? That doesn't work for any 
type of p. You can do it with a slightly fancier (and more 
dangerous) cast: `*cast(void**)&s`.

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Friday, 9 January 2015 at 18:35:56 UTC, anonymous wrote:
 On Friday, 9 January 2015 at 18:25:42 UTC, John Colvin wrote:
 struct S
 {
    void* p;
 }

 void main()
 {
    S s;
    auto a = cast(void*)s; //Error: e2ir: cannot cast s of type 
 S to type void*
 }

 Is there are a good reason for this being disallowed?

 You'd expect `cast(void*)s == s.p`? That doesn't work for any 
 type of p.

I was expecting it to work regardless of the type of p. I have an 
8 byte (on x86_64) struct which I want to reinterpret as a void*

 You can do it with a slightly fancier (and more dangerous) 
 cast: `*cast(void**)&s`.

Yuk. Better than nothing though. Thanks :)

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 1/9/15 1:50 PM, John Colvin wrote:
 On Friday, 9 January 2015 at 18:35:56 UTC, anonymous wrote:
 On Friday, 9 January 2015 at 18:25:42 UTC, John Colvin wrote:
 struct S
 {
    void* p;
 }

 void main()
 {
    S s;
    auto a = cast(void*)s; //Error: e2ir: cannot cast s of type S to
 type void*



This is actually a compiler bug! I will check to make sure it's not 
already filed, and file if it's not. However, I don't think the code 
should work, it just shouldn't print e2ir.

 }

 Is there are a good reason for this being disallowed?

 You'd expect `cast(void*)s == s.p`? That doesn't work for any type of p.

 I was expecting it to work regardless of the type of p. I have an 8 byte
 (on x86_64) struct which I want to reinterpret as a void*

 You can do it with a slightly fancier (and more dangerous) cast:
 `*cast(void**)&s`.

 Yuk. Better than nothing though. Thanks :)

This is what reinterpret_cast from C++ does.

-Steve

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Friday, 9 January 2015 at 19:03:04 UTC, Steven Schveighoffer 
wrote:
 On 1/9/15 1:50 PM, John Colvin wrote:
 On Friday, 9 January 2015 at 18:35:56 UTC, anonymous wrote:
 On Friday, 9 January 2015 at 18:25:42 UTC, John Colvin wrote:
 struct S
 {
   void* p;
 }

 void main()
 {
   S s;
   auto a = cast(void*)s; //Error: e2ir: cannot cast s of 
 type S to
 type void*



 This is actually a compiler bug!

So it is! The same happens with e.g. casting void* to string. 
Annoyingly it passes __traits(compiles, ...)

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 01/09/2015 10:25 AM, John Colvin wrote:
 struct S
 {
      void* p;
 }

 void main()
 {
      S s;
      auto a = cast(void*)s; //Error: e2ir: cannot cast s of type S to
 type void*
 }

 Is there are a good reason for this being disallowed?

I know two options:

a)

     alias p this;

b)

     auto opCast(T : void*)()
     {
         return p;
     }

Ali