On Wednesday, 28 September 2016 at 20:16:08 UTC, Walter Bright
wrote:
On 9/28/2016 6:58 AM, Timon Gehr wrote:
An excellent example of that is the std.regex package.
It's actually a bad example, because it is irrelevant: it is
obviously a bad
idea to implement regex using operator overloading, because
the regex operators
have no D equivalent.
Yet this "obviously bad" idea regularly resurfaces as a cool
use of expression templates and respected people in the
industry like it and advocate it.
Assume I have two symbolic expressions a and b:
Expression a=variable("a"), b=variable("b");
Why should I be allowed to do
auto c = a + b; // symbolic value a + b
but not
auto d = a <= b; // symbolic value a <= b
Because there is no way to stop the former but still have
operator overloading.
The fact that it's not possible to overload < but have to use the
ternary opCmp is even a performance problem. All std algorithms
only use less as a predicate, leading to lots of unnecessary
cycles when e.g. sorting UDTs.
While I agree with your point on expression templates,
overloading comparison operators has valid use cases.
