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digitalmars.D.learn - "if" is not evaluated for fields of Class.tupleof

reply Timoses <timosesu gmail.com> writes:
Hey there,

trying to read data into the fields of a class.

This is what I got so far:

```
import std.traits;
import std.bitmanip;

class Test {
     byte[4] marray;
     byte mbyte;

     this(ubyte[] data)
     {
         auto fields = this.tupleof;

         foreach (field; fields)
         {
             // Here it should actually not enter when field is 
mbyte (byte)
             if (isStaticArray!(typeof(field)))
             {
                 for (int i = 0; i < field.length; i++)
                     field[i] = data.read!(typeof(field[i]));
             }
             else
             {

             }
         }
     }
}

void main() {
     new Test([0x12, 0x23, 0x34, 0x45, 0x56]);
}
```

The problem is that `isStaticArray` won't halt when the field is 
`byte`.

When I add a `writeln(isStaticArray!(typeof(field)));` it will 
write `false` for `mbyte` though...

What's the problem? Is it a bug?

And: Is there a better way to do what I'm trying to do?...
May 19
parent reply ag0aep6g <anonymous example.com> writes:
On 05/19/2017 03:46 PM, Timoses wrote:
          foreach (field; fields)
          {
              // Here it should actually not enter when field is mbyte 
 (byte)
              if (isStaticArray!(typeof(field)))
You probably want `static if` here. With normal `if`, the body still gets compiled, even if the condition is compile-time constant false. With `static if`, the body is skipped.
May 19
parent reply Timoses <timosesu gmail.com> writes:
The easiest way is probably casting:

```
import std.traits;
import std.bitmanip;

class Test {
     byte[4] marray;
     byte mbyte;
}

void main() {
     auto value = [0x12, 0x23, 0x34, 0x45, 0x56];
     auto test = cast(Test*) value.ptr;
}
```
May 22
parent Stanislav Blinov <stanislav.blinov gmail.com> writes:
On Tuesday, 23 May 2017 at 06:42:55 UTC, Timoses wrote:
 The easiest way is probably casting:

 ```
 import std.traits;
 import std.bitmanip;

 class Test {
     byte[4] marray;
     byte mbyte;
 }

 void main() {
     auto value = [0x12, 0x23, 0x34, 0x45, 0x56];
     auto test = cast(Test*) value.ptr;
 }
 ```
Don't cast arbitrary types to classes, you're going to stumble upon very nasty surprises :) I guess you meant struct? Classes in D are quite fat, and don't start with data members right away, bookkeeping ClassInfo data comes first.
May 23