UDAs - Restrict to User Defined Types?

[Adam D. Ruppe]

On Friday, 9 November 2012 at 05:25:12 UTC, Jonathan M Davis 
wrote:
> Given that a range requires a very specific set of functions, I 
> find it highly unlikely that anything which isn't a range will
> qualify as one.


I've had it happen to me several times. Let me show you some code

from my dom.d:

mixin template JavascriptStyleDispatch() {
         string opDispatch(string name)(string v = null) if(name 
!= "popFront") { // popFront will make this look like a range. Do 
not want.


class Element {
         // name != "popFront" is so duck typing doesn't think 
it's a range
         @property string opDispatch(string name)(string v = null) 
if(name != "popFront") {
}

struct CssRule {

         string opDispatch(string nameGiven)(string value = null) 
if(nameGiven != "popFront") {
}



 From prototype.d:

class PrototypeObject {
         // the constraint is needed otherwise the Variant 
constructor fails
         @property ref PrototypeObject opDispatch(string name)() 
if(name != "length") {
}

(I'm not sure if this last one is a range problem, because it was 
Variant that was confused, but the dom ones definitely were).


Of course, they all have something in common: an open opDispatch. 
But that's a valid D feature so surely I'm not the only one using 
it.


Every one of those constraints come from it actually being a 
problem at one point or another.