Can we get rid of opApply?

[Andrei Alexandrescu]

Max Samukha wrote:
> On Tue, 20 Jan 2009 12:23:58 +0300, "Denis Koroskin"
> <2korden at gmail.com> wrote:
> 
>> One nice thing that opApply capable of is it can avoid heap activity by stack-allocating data during iteration.
>>
>> For example, given an array of ints, iterate over string representations of them:
>>
>> struct IntegersAsString
>> {
>>    void opAplly(int delegate(string s) dg)
>>    {
>>        char[16] temp;
>>
>>        foreach (i; array) {
>>            int len = sprintf(temp, "%d", i);
>>            int result = dg(temp[0..len]);
>>            if (result != 0) {
>>                return result;
>>            }
>>        }
>>
>>        return 0;
>>    }
>>
>>    private int[] array;
>> }
>>
>> int array = [1, 1, 2, 3, 5, 8, 13];
>>
>> // no heap allocation take place
>> foreach (string s; IntegersAsString(array)) {
>>    writeln(s);
>> }
>>
>> How would you do that with ranges?
> 
> struct IntegersAsString
> {
>     private
>     {
>       int[] array;
>       char[16] temp;
>     }
> 
>     char[] head()
>     {
>         int len = sprintf(temp.ptr, "%d", array[0]);
>         return temp[0..len];
>     }
> 
>     void next()
>     {
>         array = array[1..$];
>     }
> 
>     bool empty()
>     {
>         return array.length == 0;
>     }
> }
> 
> void main()
> {
>     int[] array = [1, 1, 2, 3, 5, 8, 13];
> 
>     // no heap allocation take place
>     foreach (char[] s; IntegersAsString(array))
>         writefln(s);
> }

One of these days I need to learn the algorithm:

1. Wake up

2. Get coffee

3. Read _all_ posts

4. Post only if necessary


Andrei