Array slice length confusion

[Tim Matthews]

Steven Schveighoffer wrote:
> On Wed, 08 Jul 2009 02:48:31 -0400, Tim Matthews 
> <tim.matthews7 at gmail.com> wrote:
> 
>> Was this a design choice, bug, undefined behavior, etc...?
> 
> design choice.
> 
> A slice *is* an array in the current design.  Increasing the length may 
> or may not make a copy of it.  An array slice doesn't know it was 
> originally part of another array (i.e. there are no references back to 
> the original array) so how would it know that there is data around it?  
> The only exception is appending to a prefix slice.  If a slice starts at 
> the front of an allocated array, the runtime cannot tell that it was not 
> the original array, so it clobbers data that was in the original array:
> 
> char[] str = "blah".dup;
> char[] sl = str[0..1];
> sl ~= "r";
> assert(str == "brah");
> 
> BTW, all of this is defined behavior, see 
> http://www.digitalmars.com/d/2.0/arrays.html#resize
> 
> -Steve

I thought a slice would behave slighty different due to some sort of 
meta data that is a separate area of memory so it doesn't effect D's abi.

Anyway if anyone gets here through a search engine the correct code 
assuming you can guarantee it is a slice and that doesn't go out of 
bounds. It is a systems language after all :)

module test;

import std.stdio;

void resizeView(T)(ref T[] slice, size_t newLength)
{
     (cast(size_t*)(&slice))[0] = newLength;
}

void main()
{
     char[5] a = "hello";
     char[] b = a[1..3];
     writeln(a); //(hello)
     writeln(b); //(el)
     resizeView(b, b.length+1);
     writeln(a); //(hello)
     writeln(b); //(ell)
}