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digitalmars.D - toHash /opCmp for builtin-types

reply Simon Buerger <krox gmx.net> writes:
Following came to my mind while coding some generic collection 
classes: The toHash and opCmp operations are not supported for 
builtin-types though their implementation is trivial.

* toHash
The code is already there inside TypeInfo.getHash. But 
typeid(value).getHash(&value) is much uglier than value.toHash. Note 
that hashes make sense for integer (trivial implementation), not 
necessarily for floats.

* opCmp
Would be useful for delegating opCmp of a struct to one member. 
Alternative: Introduce new operator which returns 1/0/-1 (ruby does 
this with "<=>"). Currently I end up writing:

int opCmp(...)
{
     if(a>b) return +1;
     if(a==b) return 0;
     return -1;
}

which uses 2 comparisons where only 1 is needed (though the compiler 
might notice it if comparision is pure and so on).

Furthermore it might me a nice idea to have toString (or the future 
"writeTo") for builtin-types. It would need some new code in the 
core-lib, but could simplify generic programming.

any thoughts?

- Krox
Feb 21 2011
parent reply Daniel Gibson <metalcaedes gmail.com> writes:
Am 21.02.2011 20:59, schrieb Simon Buerger:

 Following came to my mind while coding some generic collection classes:
 The toHash and opCmp operations are not supported for builtin-types
 though their implementation is trivial.

 * toHash
 The code is already there inside TypeInfo.getHash. But
 typeid(value).getHash(&value) is much uglier than value.toHash. Note
 that hashes make sense for integer (trivial implementation), not
 necessarily for floats.

 * opCmp
 Would be useful for delegating opCmp of a struct to one member.
 Alternative: Introduce new operator which returns 1/0/-1 (ruby does this
 with "<=>"). Currently I end up writing:

 int opCmp(...)
 {
 if(a>b) return +1;
 if(a==b) return 0;
 return -1;
 }

 which uses 2 comparisons where only 1 is needed (though the compiler
 might notice it if comparision is pure and so on).

 Furthermore it might me a nice idea to have toString (or the future
 "writeTo") for builtin-types. It would need some new code in the
 core-lib, but could simplify generic programming.

 any thoughts?

 - Krox



Well, opCmp() can be done easier, at least for ints:

int opCmp(...) {
	return a-b;
}

For floats.. well, if you don't want/need any tolerance this would work 
as well, else it'd be more difficult.

A <=> operator would be neat, though.
Feb 21 2011
parent reply Simon Buerger <krox gmx.net> writes:
On 21.02.2011 21:22, Daniel Gibson wrote:

 Am 21.02.2011 20:59, schrieb Simon Buerger:

 Following came to my mind while coding some generic collection classes:
 The toHash and opCmp operations are not supported for builtin-types
 though their implementation is trivial.

 * toHash
 The code is already there inside TypeInfo.getHash. But
 typeid(value).getHash(&value) is much uglier than value.toHash. Note
 that hashes make sense for integer (trivial implementation), not
 necessarily for floats.

 * opCmp
 Would be useful for delegating opCmp of a struct to one member.
 Alternative: Introduce new operator which returns 1/0/-1 (ruby does
 this
 with "<=>"). Currently I end up writing:

 int opCmp(...)
 {
 if(a>b) return +1;
 if(a==b) return 0;
 return -1;
 }

 which uses 2 comparisons where only 1 is needed (though the compiler
 might notice it if comparision is pure and so on).

 Furthermore it might me a nice idea to have toString (or the future
 "writeTo") for builtin-types. It would need some new code in the
 core-lib, but could simplify generic programming.

 any thoughts?

 - Krox



 Well, opCmp() can be done easier, at least for ints:

 int opCmp(...) {
 return a-b;
 }



sadly no: (-3000000000) - (3000000000) = -170532704 which is 
incorrect. It does however work for short/byte (and opCmp still 
returning int).


 For floats.. well, if you don't want/need any tolerance this would
 work as well, else it'd be more difficult.



I'm not sure if it make sense for floats. Furthermore, does 
TypeInfo.getHash support them?


 A <=> operator would be neat, though.
Feb 21 2011
parent reply Simon Buerger <krox gmx.net> writes:
 sadly no: (-3000000000) - (3000000000) = -170532704 which is
 incorrect. It does however work for short/byte (and opCmp still
 returning int).



oops, wrong example. It is: (-2000000000) - (2000000000) = 294967296, 
sry. Anyway, you see the point with overflows
Feb 21 2011
parent Daniel Gibson <metalcaedes gmail.com> writes:
Am 21.02.2011 21:55, schrieb Simon Buerger:

 sadly no: (-3000000000) - (3000000000) = -170532704 which is
 incorrect. It does however work for short/byte (and opCmp still
 returning int).



 oops, wrong example. It is: (-2000000000) - (2000000000) = 294967296,
 sry. Anyway, you see the point with overflows



Hm yes, you're right :-)
Feb 21 2011