How would you do this in D?

[Jonathan M Davis]

On 2011-05-10 17:32, Jose Armando Garcia wrote:
> Hey guys,
> 
> I am trying to create a function that return true or executes
> "something" the n-th time it is called from a specific call site. How
> would you do that in D? In C we can do that with the help of
> pre-processor macros. E.g.:
> 
> ---
> #include <assert.h>
> 
> #define EVERY(N, ACTION) { static int counter = 0; if(++counter > (N))
> counter -= (N); if(counter == 1) (ACTION); }
> 
> int main()
> {
>    int i = 0;
>    int j = 0;
>    while(i < 10)
>    {
>       EVERY(10, ++j);
>       EVERY(2, ++i);
>    }
>    assert(j == 2);
>    assert(i == 10);
> }
> ---
> 
> In D, I hacked the following implementation. I don't like this
> implementation for a log of reason... Am I missing some D feature? Can
> someone do better?
> 
> ---
> int[string] map;
> 
> bool every(string file = __FILE__, int line = __LINE__)(int time)
> {
>    // assume file ~ "+" ~ to!string(line) is unique
>    // assumption could be removed by using a struct
>    string key = file ~ "+" ~ to!string(line);
> 
>    map[key] += 1;
>    if(map[key] > time) map[key] -= time;
> 
>    return map[key] == 1;
> }
> 
> unittest
> {
>    auto i = 0;
>    auto j = 0;
>    while(i < 10)
>    {
>       if(every(10)) ++j;
>       if(every(2)) ++i;
>    }
>    assert(j == 2);
>    assert(i == 10);
> }
> 
> void main() {}
> ---

My suggestion would be to use a string mixin. It would do essentially the same 
thing that the macro does.

- Jonathan M Davis