Passing dynamic arrays

[Steven Schveighoffer]

On Mon, 08 Nov 2010 14:22:36 -0500, Ali Çehreli <acehreli at yahoo.com> wrote:

> Steven Schveighoffer wrote:
>  > On Mon, 08 Nov 2010 13:35:38 -0500, Daniel Gibson
>  >> If you pass a dynamic array to a function and chance it's size within
>  >> the function, you have undefined behaviour - you never know if it  
> will
>  >> affect the original array (from the calling function) or not.
>  >
>  > Not exactly.  If you happen to change its size *and* change the  
> original
>  > data afterwards, then it's somewhat undefined
>
> Let's also note that appending to the array qualifies as "change its  
> size *and* change the original data afterwards." We cannot be sure  
> whether appending affects the passed-in array.

No, it doesn't. If you are appending to data that was passed in, you are  
not changing the *original data* passed in.  You are only appending to it.

for example:

char[] s = "foo".dup;

s ~= "bar";

does not change the first 3 characters at all. So any aliases to s would  
not be affected.  However, any data aliased to the original s may or may  
not be aliased to the new s.  Once you start changing that original data  
(either via s or via an alias to the original s), this is where the  
confusing behavior occurs.

In my experience, this does not cause a problem in the vast majority of  
cases.

-Steve