• Regan Heath (24/24) Jun 18 2004 Is this valid:
• Vathix (5/16) Jun 18 2004 They're just not compatible types. You can't cast a struct to an int eit...
• Regan Heath (21/42) Jun 19 2004 Do you mean "an int to a struct"? Why not? All you're saying is pretend
• =?ISO-8859-15?Q?Julio_C=E9sar_Carrascal_Urquijo?= (7/16) Jun 19 2004 Arrays in D are just a struct with a length field and a pointer to the
• Regan Heath (7/20) Jun 20 2004 Yes. And calculate the length. Is there an official way to do this? Or a...

Regan Heath <regan netwin.co.nz> writes:

Is this valid:

   ulong length = 1;
   ubyte[8] test;

   test[] = cast(ubyte[])length;
or
   test = cast(ubyte[])length;
or
   test[] = cast(ubyte[])length[0..8];
or
   ?

if not, why not?


what would it do exactly...

- convert length from a ulong to a ubyte and assign to test[0], test[1], 
test[2], ..etc..
- point ubyte's data pointer at length (or a copy of length).

I'm hoping for the latter because as ulong is 64 bit and ubyte is 8 bit 
and ubyte[8] is 64 bits worth of data it could do it.

Without this possibility you're left going:
   memcpy(&test[0],length,length.sizeof);

which, while not bad, is not true D style.

Thoughts?

Regan.

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Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

"Vathix" <vathixSpamFix dprogramming.com> writes:

"Regan Heath" <regan netwin.co.nz> wrote in message
news:opr9tddfna5a2sq9 digitalmars.com...
 Is this valid:

    ulong length = 1;
    ubyte[8] test;

    test[] = cast(ubyte[])length;
 or
    test = cast(ubyte[])length;
 or
    test[] = cast(ubyte[])length[0..8];
 or
    ?

 if not, why not?

They're just not compatible types. You can't cast a struct to an int either.
You can get around it using a pointer:

test[] = (cast(ubyte*)&length)[0 .. length.sizeof];

Regan Heath <regan netwin.co.nz> writes:

On Fri, 18 Jun 2004 21:49:52 -0400, Vathix 
<vathixSpamFix dprogramming.com> wrote:
 "Regan Heath" <regan netwin.co.nz> wrote in message
 news:opr9tddfna5a2sq9 digitalmars.com...
 Is this valid:

    ulong length = 1;
    ubyte[8] test;

    test[] = cast(ubyte[])length;
 or
    test = cast(ubyte[])length;
 or
    test[] = cast(ubyte[])length[0..8];
 or
    ?

 if not, why not?

 They're just not compatible types. You can't cast a struct to an int 
 either.

Do you mean "an int to a struct"? Why not? All you're saying is pretend 
this is one of these, all it has to do is point at the address given and 
interpret it as the new type.


So I don't see why this:

   test[] = cast(ubyte[])length;

should not be allowed, it's explicit, and it makes sense that it should do 
exactly this:

   test[] = (cast(ubyte*)&length)[0 .. length.sizeof];


Given that you know the size of each type you could cast any array of any 
basic type to any other array of another basic type, or even a user 
defined type.

Casting from a small type to a large type creates the case where there 
isn't enough data to make up a complete last item, in this case you can 
either pad or throw an "Error: lengths don't match for array copy" error.

I think this is very useful.

 You can get around it using a pointer:

 test[] = (cast(ubyte*)&length)[0 .. length.sizeof];

Thanks. This will help for now. But pointers really aren't the D thing.

Regan.

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Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

=?ISO-8859-15?Q?Julio_C=E9sar_Carrascal_Urquijo?= writes:

Regan Heath wrote:

 On Fri, 18 Jun 2004 21:49:52 -0400, Vathix 
 <vathixSpamFix dprogramming.com> wrote:
 They're just not compatible types. You can't cast a struct to an int 
 either.

 
 Do you mean "an int to a struct"? Why not? All you're saying is pretend 
 this is one of these, all it has to do is point at the address given and 
 interpret it as the new type.

Arrays in D are just a struct with a length field and a pointer to the 
data. So what you need to do is change the pointer so that it points to 
the address where the ulong is stored.


-- 
Julio César Carrascal Urquijo
http://jcesar.f2o.org/

Regan Heath <regan netwin.co.nz> writes:

On Sat, 19 Jun 2004 12:31:57 -0500, Julio César Carrascal Urquijo 
<adnoctum phreaker.net> wrote:

 Regan Heath wrote:

 On Fri, 18 Jun 2004 21:49:52 -0400, Vathix 
 <vathixSpamFix dprogramming.com> wrote:

  >>
 They're just not compatible types. You can't cast a struct to an int 
 either.

 Do you mean "an int to a struct"? Why not? All you're saying is pretend 
 this is one of these, all it has to do is point at the address given 
 and interpret it as the new type.

 Arrays in D are just a struct with a length field and a pointer to the 
 data. So what you need to do is change the pointer so that it points to 
 the address where the ulong is stored.

Yes. And calculate the length. Is there an official way to do this? Or are 
you suggesting an ugly hack?

Regan.

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