Behavior of "auto"

[Derek Parnell]

On Thu, 6 Dec 2007 06:20:53 +0000 (UTC), NullTerminator wrote:

> == Repost the article of NullTerminator (NullTerminator at Hotmail.com)
> == Posted at 2007/12/06 01:07 to D
> 
> A strange effect of using auto:
> 
> The following code:
> import std.stdio;
> 
> class Test {
>    this() {
>       printf("Created\n");
>    }
> 
>    ~this() {
>       printf("Destroyed\n");
>    }
> }
> 
> int main(char[][] args){
>    for (int n = 0; n < 10; n++)
>       Test t = new Test();
>    return 0;
> }
> 
> produces the following output:
> Created
> Created
> Created
> Created
> Created
> Created
> Created
> Created
> Created
> Created
> Destroyed
> Destroyed
> Destroyed
> Destroyed
> Destroyed
> Destroyed
> Destroyed
> Destroyed
> Destroyed
> Destroyed
> 
> where as changing the line:
>       Test t = new Test();
> to:
>       auto Test t = new Test();
> produces:
> Created
> Destroyed
> Created
> Destroyed
> Created
> Destroyed
> Created
> Destroyed
> Created
> Destroyed
> Created
> Destroyed
> Created
> Destroyed
> Created
> Destroyed
> Created
> Destroyed
> Created
> Destroyed
> 
> As I understand it, one would expect this to be the effect of "scope," not
> "auto."  Can someone explain why this happens?

Both 'scope' and 'auto' are poorly documented. However, the variable
declared with an 'auto' is scoped to the block it is declared in and is
destroyed when going out of scope. In effect 'auto' is shorthand for 'scope
<type>' ...

That is to say ...

  auto t = new Test();

is equivalent to ...

  scope Test t = new Test();
   

-- 
Derek
(skype: derek.j.parnell)
Melbourne, Australia
6/12/2007 5:51:16 PM