Array operations -- not actually so difficult

[Don Clugston]

Array operations are one of the very few 2.0 features that haven't made 
it into 1.0. My experiments into expression templates suggest that it 
might not be very complicated after all.

Consider something like a dot product,

real a[], b[], c[];
real d = dot(a+b, c);

For performance, it would be better if the compiler actually *didn't* 
evaluate a+b. Instead, that should compile to:

real sum = 0;
for (int i=0; i<c.length; ++i) {
      sum+=(a[i]+b[i])*c[i];
}
d=sum;

In fact, we could create a fantastic library implementation of array 
operations with a tiny bit of syntactic sugar:
instead of generating an error message for array operations, look for an 
opXXX function, and treat it the same way the implicit array properties 
work.
----------
void opMulAssign(real [] a, real w)
{
     for(int i=0; i<a.length; ++i) { a[i]*=w; }
}

void main()
{
     real b[] = [1.0L, 2, 3, 4];
     b.opMulAssign(3.5); // OK.
     b *= 3.5; // Fails with "Error: 'b' is not a scalar, it is a real[]"
}
----------
So the message to Walter is, support for array operations will not 
require any change to the back end. They are just a bit of syntactic 
sugar at the front end.