"+=" (overloads) with custom array slices on both lhs, and rhs ??

[Ali Çehreli]

On 9/5/21 12:43 PM, james.p.leblanc wrote:

 > I have constructed a custom array type that works, but is missing
 > correct functioning on some operator overloads.

With its old, new, and newest styles; and support for multi-dimensional 
use cases; operator overloading can be difficult to get right. Here is a 
one-dimensional case that works:

struct MyArray(T) {
   T[] elements;

   this(size_t length) {
     this.elements.length = length;
   }

   size_t opDollar() const {
     return elements.length;
   }

   auto opSliceOpAssign(string op)(T value, size_t beg, size_t end) {
     auto slice = elements[beg .. end];
     mixin (format!q{
         slice[] %s= value;
       }(op));
     return slice;
   }

   // For the entire range of elements
   auto opSliceOpAssign(string op)(T value) {
     // Dispatch to the other one
     return this.opSliceOpAssign!op(value, 0, elements.length);
   }
}

import std.stdio;
import std.format;

void main() {
   auto m = MyArray!(int)(10);

   m[2 .. 5] += 42;
   writeln(m);

   m[4 .. $] -= 100;
   writeln(m);

   m[] *= 2;
   writeln(m);
}

Ali