Re: Enums and immutables

[ag0aep6g via Digitalmars-d-learn]

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.

Re: Enums and immutables

[rikki cattermole via Digitalmars-d-learn]

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[].

Enums and immutables

[Oleg B via Digitalmars-d-learn]

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?