digitalmars.D - [Suggestion] .toHash and .toString on built-in types
- Stewart Gordon <smjg_1998 yahoo.com> Nov 15 2004
I've noticed that the hashmap template I created a while back only works with struct/union/class types and not with primitive/array/pointer types. Basically, we have a limitation on the generic programming side: the .toHash property is only definable on struct/union/class types, and doesn't exist on built-in ones. I cannot change it to dig into TypeInfo, since half the point of my template is to be a workaround for the failings of D's AAs. TypeInfo hacking is a rather down and dirty approach anyway; even once the shortfalls are dealt with, key.toHash will remain a nicer notation than typeid(KeyType).getHash(&key). The .toHash property would correspond to the existing hash function for the relevant type. The only issue I see is what should happen with pointer types. Possibilities I can see are: (a) Keep TypeInfo_P.getHash returning the memory address, and have pointer.toHash follow this convention. But this would make an exception to the rule that pointer.anything is equivalent to (*pointer).anything. (b) Redefine the hash of a pointer (except void*) to be equal to the hash of the dereferenced data. Not sure if this would be the Right Thing, as any container that uses pointers as keys would be invalidated if the data they point to is modified. (c) Keep the TypeInfo (and hence the behaviour in built-in AAs) as it is, but nonetheless have pointer.toHash equivalent to (*pointer).toHash. This wouldn't break existing code, but would require that a given template consistently uses either .toHash or TypeInfo.getHash. And this is before you get back into arguing over the propriety of using memory addresses as hash values. Similarly, every type having a .toString property might be handy, and it would correspond to the behaviour of the "%s" format specifier on the type involved. Well, maybe open to the same debates.... Just thinking about it, I guess it's a matter of debate whether these features would really achieve anything over fixing some bugs.... Stewart.
Nov 15 2004