I don't get how I can create a dynamic array of Cycle buffers of size 2 which use a struct.

 struct ms {
   int a;
   int b;
 }
 ms[2] msBuffer;
 alias circularStructBuffersT = typeof(cycle(msBuffer));
 circularStructBuffersT[int] circularStructBuffers;

 int i = 2;
 auto x = circularStructBuffers.require(i, (){
   ms[2] t;
   return cycle(t,2);
 });

This give an error:

Error: template object.require cannot deduce function from argument types !()(Cycle!(ms[2])[int], int, Cycle!(ms[2]) function() pure nothrow @nogc @system), candidates are:
/Library/D/dmd/src/druntime/import/object.d(3225):        require(K, V)(ref V[K] aa, K key, lazy V value = V.init)

Not sure if the `m[2] t` survives the scope exit in form of a closure (?) or if cycle takes a reference to it...

-- 
Robert M. Münch
http://www.saphirion.com
smarter | better | faster

On 2/22/20 2:29 PM, Robert M. Münch wrote:
> I don't get how I can create a dynamic array of Cycle buffers of size 2 which use a struct.
> 
>   struct ms {
>     int a;
>     int b;
>   }
>   ms[2] msBuffer;
>   alias circularStructBuffersT = typeof(cycle(msBuffer));
>   circularStructBuffersT[int] circularStructBuffers;
> 
>   int i = 2;
>   auto x = circularStructBuffers.require(i, (){
>     ms[2] t;
>     return cycle(t,2);
>   });

It looks like require() requires :) a value, which it evaluates only if necessary:

  https://dlang.org/spec/hash-map.html#inserting_if_not_present

In your case, you're passing a callable. All you need to do is to actually call that callable with empty parenthesis:

  auto x = circularStructBuffers.require(i, {
    // ...
    }());  // <-- HERE

Because the parameter is lazy, it will still be called only when needed.

Ali