D's definitions of "is" and "==" have so much redundency. That might indicate some flaw. If references and values (for classes and arrays) could be clearly distinguished in the syntax, the "is" operator is not necessary at all.
A related thing is element-wise operation. Consider string[] a; string[] b; string[] c; ... c[1..3]=a[1..3]~b[1..3]; and, int[] a; int[] b; int[] c; ... c[1..3]=a[1..3]+b[1..3]; The two pieces are very much similar, and I expect similar results. But D doesn't provide element-wise concatenation, because it's not clear in the syntax whether a[1..3] is a reference (for simple array concatenation) or a value (for element-wise concatenation).
