• monarch_dodra (41/41) Jul 02 2012 When I read the "D programming language" chapter on operator
• Andrei Alexandrescu (3/10) Jul 02 2012 I agree. There should be an enhancement request for this.

"monarch_dodra" <monarch_dodra gmail.com> writes:

When I read the "D programming language" chapter on operator 
overloading, I found that the fact there were operators 
"opIndexAssign", "opIndexOpAssing" and "opIndexUnary" to be 
nothing short of brilliant. Finally, a container of bools that 
works for real!

However, if and when "opIndex" is capable of returning a 
reference, isn't defining the above symbols gratuitous, error 
prone, and worse, actually restrictive?

Case in point:
----
import std.container;
import std.stdio;

void main()
{
   Array!int ai;
   ai.length = 3;

   ++ai[0];           //Does not compile because the 
implementation forgot to define opIndexUnary
   ai[0] = ai[1] = 5; //Does not compile because opIndexAssign 
does not return a value
   ++(++ai[0]);       //Can't compile (even if opIndexUnary 
existed)
   (ai[0] += 5) += 5; //Can't compile
}
----
Here, there are 4 lines: The first doesn't compile simply because 
we forgot to define the operator in the class. The second because 
the return value of OpIndexAssign is defined as void. Finally, 
the third and fourth simply can't compile, because 
"opIndexOpAssing" and "opIndexUnary" can't be chained, at least 
not without extra language support (and even then, you'd have to 
pay for re-indexing every time).

If Array simply defined "ref T opIndex(size_t i)" (which it is 
perfectly capable of doing), and didn't define anything else, 
then all of the above would work. Lines 1 & 2 don't work because 
of implement details, but can be fixed. 3 & 4 simply can't be 
fixed.

In the case of containers that are capable of returning refs, is 
there really a point to rolling out more code, just to get less?

(This, of course, does not hold for Array!bool, or any other 
container that can't return refs)

Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:

On 7/2/12 4:13 AM, monarch_dodra wrote:
 When I read the "D programming language" chapter on operator
 overloading, I found that the fact there were operators "opIndexAssign",
 "opIndexOpAssing" and "opIndexUnary" to be nothing short of brilliant.
 Finally, a container of bools that works for real!

 However, if and when "opIndex" is capable of returning a reference,
 isn't defining the above symbols gratuitous, error prone, and worse,
 actually restrictive?

I agree. There should be an enhancement request for this.

Andrei