Idea: Immutable blocks within functions

[Xinok]

On Saturday, 7 September 2013 at 23:05:31 UTC, Peter Alexander 
wrote:
> On Saturday, 7 September 2013 at 22:57:40 UTC, Xinok wrote:
>> 	immutable
>> 	{
>> 		int[] arr = ...;
>> 		int[] arr2 = arr.dup;
>> 		sort(arr); // arr is still mutable
>> 		
>> 		int[] arr2 = arr.dup;
>> 		reverse(arr2);
>> 		arr ~= arr2;
>> 	}
>
> How do you stop mutable references escaping in functions called 
> from the immutable block?
>
> e.g.
>
> int* p;
> void foo(ref int x) { p = &x; }
>
> void main()
> {
>     immutable
>     {
>         int x = 1;
>         foo(x);
>     }
>     *p = 0;
> }

Immutable blocks would have the same restrictions as pure 
functions. And like pure functions, you could only call other 
pure functions. Since foo is not pure, this code wouldn't compile.