What is going on in this code?

[Carlin via Digitalmars-d]

On Thursday, 14 April 2016 at 10:29:43 UTC, ag0aep6g wrote:
> On 14.04.2016 12:14, Carlin wrote:
>> import std.stdio;
>> import std.bitmanip;
>>
>> ubyte[] serialize(uint t)
>> {
>>      ubyte[] bytes = nativeToBigEndian(t);
>>      return bytes;
>> }
>>
>> void main()
>> {
>>      writeln(serialize(0));
>> }
>
> Your code is wrong. It's really easy to get wrong, though. Too 
> easy probably.
>
> nativeToBigEndian returns a fixed-size array. That's a value 
> type. By assigning it to a ubyte[], you're slicing the return 
> value. That is, you make a reference to temporary data. The 
> reference becomes invalid as soon the assignment is over, so 
> you're returning a slice to garbage memory.
>
> To make a ubyte[] from the result of nativeToBigEndian, you 
> have to dup it:
> ----
> ubyte[] serialize(uint t)
> {
>     return nativeToBigEndian(t).dup;
> }
> ----

Thanks, that works perfectly! I couldn't figure it out and I knew 
I had to be missing something really basic. I still don't 
understand though why it works in release but not in debug.