Problem with closures

[Chris Nicholson-Sauls]

Lutger wrote:
> Alain wrote:
>> Frits van Bommel Wrote:
>>
>>> Alain wrote:
>>>> AddFunc addN(int n) {
>>>>     int add(int i) {
>>>>         return i + n;
>>>>     }
>>>>     return &add; // the add function captured will remember the 
>>>> value of n
>>>> }
>>> [snip]
>>>> Am i missing something?
>>> You shouldn't return delegates to nested functions, just like you 
>>> shouldn't return pointers to local variables.
>>> Delegates to nested functions contain a pointer to the stack frame of 
>>> the enclosing function. If that function has returned, the stack 
>>> frame may be corrupted (especially if you have called another 
>>> function, like apply(), since then).
>>
>> How come this compiles? Is it a bug ?
>>
>> Alain
> 
> This is valid code. It is up to the programmer to make sure the delegate 
>  doesn't use vars that are out of scope. There was some talk about this, 
> to copy the 'evironment' for later use, it might be solved in the future.
> 
> std.bind might be of use here.

As could a template.

<code>
import std .stdio ;

alias int delegate(int n) AddFunc;

template TAddN (int N) {
   const TAddN = (int i) { return i + N; } ;
}

void apply (int[] array, AddFunc func) {
   foreach (inout i; array) {
     i = func(i);
   }
}

void main () {
     int[] numbers = [1,2,3] ;

     writefln("numbers before = ", numbers);
     apply(numbers, TAddN!(40));
     writefln("numbers after = ", numbers);
}
</code>

-- Chris Nicholson-Sauls