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digitalmars.D.learn - Enums and immutables

reply Oleg B <code.viator gmail.com> writes:
Hello. I found strange behavior while casting enum array and 
immutable array.

import std.stdio;

void main()
{
     enum arr = cast(ubyte[])[0,0,0,1,0,0,0,2,0,0,0,3,0,0,0,4];

     auto arr1 = cast(void[])arr;
     immutable arr2 = cast(immutable(void)[])arr;
     enum arr3 = cast(void[])arr;

     writeln(cast(ushort[])arr1); // [0, 256, 0, 512, 0, 768, 0, 
1024]
     writeln(cast(ushort[])arr2); // [0, 256, 0, 512, 0, 768, 0, 
1024]
     writeln(cast(ushort[])arr3); // [0, 0, 0, 1, 0, 0, 0, 2, 0, 
0, 0, 3, 0, 0, 0, 4]
}

I think it's related to representation of enums by compiler as 
#define.
It's right? It's behavior by design?
Mar 18
next sibling parent rikki cattermole <rikki cattermole.co.nz> writes:
On 19/03/2017 1:22 AM, Oleg B wrote:
 Hello. I found strange behavior while casting enum array and immutable
 array.

 import std.stdio;

 void main()
 {
     enum arr = cast(ubyte[])[0,0,0,1,0,0,0,2,0,0,0,3,0,0,0,4];

     auto arr1 = cast(void[])arr;
     immutable arr2 = cast(immutable(void)[])arr;
     enum arr3 = cast(void[])arr;

     writeln(cast(ushort[])arr1); // [0, 256, 0, 512, 0, 768, 0, 1024]
     writeln(cast(ushort[])arr2); // [0, 256, 0, 512, 0, 768, 0, 1024]
     writeln(cast(ushort[])arr3); // [0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 3,
 0, 0, 0, 4]
 }

 I think it's related to representation of enums by compiler as #define.
 It's right? It's behavior by design?
It took me a bit but what I thinking happening is 1 and 2 are being casted at runtime where as 3 is at CT. At CT its per value of the enum array, at RT its per x bytes from array. Which sort of makes sense as at CT it does know the type even if you did cast it to void[].
Mar 18
prev sibling parent ag0aep6g <anonymous example.com> writes:
On 03/18/2017 01:22 PM, Oleg B wrote:
     enum arr = cast(ubyte[])[0,0,0,1,0,0,0,2,0,0,0,3,0,0,0,4];

     auto arr1 = cast(void[])arr;
     immutable arr2 = cast(immutable(void)[])arr;
     enum arr3 = cast(void[])arr;
Aside: The casts here do nothing to affect the outcome.
     writeln(cast(ushort[])arr1); // [0, 256, 0, 512, 0, 768, 0, 1024]
     writeln(cast(ushort[])arr2); // [0, 256, 0, 512, 0, 768, 0, 1024]
     writeln(cast(ushort[])arr3); // [0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 3,
 0, 0, 0, 4]
I guess the last one here is supposed to be the surprising one. I find them all surprising, actually. `arr` itself is already not what I'd expect. It should be an array with 64 elements, because you're casting an array of 16 int elements to ubyte[] (16 * int.sizeof = 64). At least that's how it works with a run-time array: auto a = [0,0,0,1,0,0,0,2,0,0,0,3,0,0,0,4]; auto b = cast(ubyte[]) a; assert(b.length == 64); But when the source is a literal or an enum, the cast doesn't change the length. Instead the elements are casted individually. I'd call this a bug. It's definitely surprising. It's also potentially throwing data away: writeln(cast(ubyte[]) [257, 2, 3, 4]); /* [1, 2, 3, 4] */ Run-time array casts don't do that.
Mar 18