Can you fix this code to avoid using pointers?

[XavierAP via Digitalmars-d-learn]

I do not really think it's a bad solution, to check several 
scalar arguments that must obey the same condition; just 
wondering if you have better ideas. Try to avoid modifying the 
function's signature and defining custom types, unless you have a 
really terrific idea.

void calc(double in1, double in2, double in3, double in4)
in {
   foreach(const p; [&in1, &in2, &in3, &in4])
      enforce(*p > 0);
}
body { /* ... */ }