digitalmars.D.learn - Best way to compare primitive types
- Jari-Matti =?ISO-8859-1?Q?M=E4kel=E4?= (20/20) May 08 2007 Let's say I want to write a wrapper around a primitive type (it could
- Daniel Keep (22/49) May 08 2007 I imagine if you wanted to do it *properly*, you could write a templated
- Jari-Matti =?ISO-8859-1?Q?M=E4kel=E4?= (8/25) May 08 2007 Thanks for all the answers.
- Don Clugston (5/35) May 08 2007 Since there is no opUnordered(), (you can't have !<>= for UDTs) it's
- Ary Manzana (23/50) May 08 2007 Maybe something like this:
- Henning Hasemann (6/12) May 08 2007 I always write this as:
- Ary Manzana (3/20) May 08 2007 Oh... That's because I'm almost always programming in Java (int can be
- Ary Manzana (2/23) May 08 2007 Obviously I mistyped the word "can". It should be "can't".
- Jarrett Billingsley (5/13) May 08 2007 You can use:
- John Ohno (7/34) May 08 2007 You could probably cast to a void[] and opcmp that. Depends on whether y...
Let's say I want to write a wrapper around a primitive type (it could
possibly also be a class or struct, but that isn't necessary now). What's
the best way to do opCmp? I've seen there is TypeInfo.compare there
somewhere, but how does it work? I get
Error: this for compare needs to be type TypeInfo not type Foo *
Also, if it works, does it have performance problems? I read from the ng
archives that the compiler might not inline it.
Here's the stuff I'm writing:
struct Foo(T) {
T value;
// or maybe T opCmp(T other) for reals, floats etc.
// to handle NaN properly
int opCmp(T other) {
// I would like to do something like
// return builtin.opCmp(value, other.value);
// because there are so many special cases for
// the primitive types and it feels a bit stupid
// to reimplement the comparison in every wrapper
}
}
May 08 2007
Jari-Matti Mäkelä wrote:
Let's say I want to write a wrapper around a primitive type (it could
possibly also be a class or struct, but that isn't necessary now). What's
the best way to do opCmp? I've seen there is TypeInfo.compare there
somewhere, but how does it work? I get
Error: this for compare needs to be type TypeInfo not type Foo *
Also, if it works, does it have performance problems? I read from the ng
archives that the compiler might not inline it.
Here's the stuff I'm writing:
struct Foo(T) {
T value;
// or maybe T opCmp(T other) for reals, floats etc.
// to handle NaN properly
int opCmp(T other) {
// I would like to do something like
// return builtin.opCmp(value, other.value);
// because there are so many special cases for
// the primitive types and it feels a bit stupid
// to reimplement the comparison in every wrapper
}
}
I imagine if you wanted to do it *properly*, you could write a templated
compare function that uses static ifs to do comparison of atomic
numeric types, arrays of (sometype), aas of (sometype, sometype),
structs, classes, typedefs and pointers to (sometype).
Or, you could just cheat.
int opCmp(T other)
{
if( other < this ) return -1;
else if( this < other ) return 1;
else if( this == other ) return 0;
else assert(false); // you COULD get here if other is NaN
}
--
int getRandomNumber()
{
return 4; // chosen by fair dice roll.
// guaranteed to be random.
}
http://xkcd.com/
v2sw5+8Yhw5ln4+5pr6OFPma8u6+7Lw4Tm6+7l6+7D
i28a2Xs3MSr2e4/6+7t4TNSMb6HTOp5en5g6RAHCP http://hackerkey.com/
May 08 2007
Daniel Keep wrote:Jari-Matti Mäkelä wrote:Let's say I want to write a wrapper around a primitive type (it could possibly also be a class or struct, but that isn't necessary now). What's the best way to do opCmp?I imagine if you wanted to do it *properly*, you could write a templated compare function that uses static ifs to do comparison of atomic numeric types, arrays of (sometype), aas of (sometype, sometype), structs, classes, typedefs and pointers to (sometype).Or, you could just cheat. int opCmp(T other) { if( other < this ) return -1; else if( this < other ) return 1; else if( this == other ) return 0; else assert(false); // you COULD get here if other is NaN }Thanks for all the answers. Actually this is almost the same I have now. I just created another version of opCmp for types that have a NaN value and made them return NaN, not assert. Ok, I think your reply also answers my question about the builtin comparison functionality. So there isn't currently one. Wouldn't it be useful to get a "properly" done templated version into the "standard library"?
May 08 2007
Don Clugston <dac nospam.com.au> Jari-Matti Mäkelä wrote:Daniel Keep wrote:Since there is no opUnordered(), (you can't have !<>= for UDTs) it's hard to know what to do with a NaN -- I don't think it's possible to make it work sensibly. It's inevitable that it will be different to the built-in operators.Jari-Matti Mäkelä wrote:Let's say I want to write a wrapper around a primitive type (it could possibly also be a class or struct, but that isn't necessary now). What's the best way to do opCmp?I imagine if you wanted to do it *properly*, you could write a templated compare function that uses static ifs to do comparison of atomic numeric types, arrays of (sometype), aas of (sometype, sometype), structs, classes, typedefs and pointers to (sometype).Or, you could just cheat. int opCmp(T other) { if( other < this ) return -1; else if( this < other ) return 1; else if( this == other ) return 0; else assert(false); // you COULD get here if other is NaN }Thanks for all the answers. Actually this is almost the same I have now. I just created another version of opCmp for types that have a NaN value and made them return NaN, not assert.Ok, I think your reply also answers my question about the builtin comparison functionality. So there isn't currently one. Wouldn't it be useful to get a "properly" done templated version into the "standard library"?
May 08 2007
Maybe something like this:
---
int opCmp(T other) {
return this.value > other ? 1 :
(this.value < other ? -1 : 0);
}
---
Usage:
---
void main() {
Foo!(int) f1;
f1.value = 5;
writefln("%s", f1 < 6);
writefln("%s", f1 > 6);
}
---
Ouputs:
true
false
Note that for equals comparison you need to implement opEquals (I didn't
know that until I wrote the example... isn't it a bit akward?).
Jari-Matti Mäkelä escribió:
Let's say I want to write a wrapper around a primitive type (it could
possibly also be a class or struct, but that isn't necessary now). What's
the best way to do opCmp? I've seen there is TypeInfo.compare there
somewhere, but how does it work? I get
Error: this for compare needs to be type TypeInfo not type Foo *
Also, if it works, does it have performance problems? I read from the ng
archives that the compiler might not inline it.
Here's the stuff I'm writing:
struct Foo(T) {
T value;
// or maybe T opCmp(T other) for reals, floats etc.
// to handle NaN properly
int opCmp(T other) {
// I would like to do something like
// return builtin.opCmp(value, other.value);
// because there are so many special cases for
// the primitive types and it feels a bit stupid
// to reimplement the comparison in every wrapper
}
}
May 08 2007
On Tue, 08 May 2007 09:43:28 -0300
Ary Manzana <ary esperanto.org.ar> wrote:
Maybe something like this:
---
int opCmp(T other) {
return this.value > other ? 1 :
(this.value < other ? -1 : 0);
}
I always write this as:
return this.value < other ? -1 : this.value > other;
Which is more leet (read unreadable) ,-)
Henning
May 08 2007
Henning Hasemann escribió:On Tue, 08 May 2007 09:43:28 -0300 Ary Manzana <ary esperanto.org.ar> wrote:Oh... That's because I'm almost always programming in Java (int can be converted to a boolean). :-PMaybe something like this: --- int opCmp(T other) { return this.value > other ? 1 : (this.value < other ? -1 : 0); }I always write this as: return this.value < other ? -1 : this.value > other; Which is more leet (read unreadable) ,-) Henning
May 08 2007
Ary Manzana escribió:Henning Hasemann escribió:Obviously I mistyped the word "can". It should be "can't".On Tue, 08 May 2007 09:43:28 -0300 Ary Manzana <ary esperanto.org.ar> wrote:Oh... That's because I'm almost always programming in Java (int can be converted to a boolean). :-PMaybe something like this: --- int opCmp(T other) { return this.value > other ? 1 : (this.value < other ? -1 : 0); }I always write this as: return this.value < other ? -1 : this.value > other; Which is more leet (read unreadable) ,-) Henning
May 08 2007
"Jari-Matti Mäkelä" <jmjmak utu.fi.invalid> wrote in message news:f1ppgi$262c$1 digitalmars.com...Error: this for compare needs to be type TypeInfo not type Foo * struct Foo(T) { T value; // or maybe T opCmp(T other) for reals, floats etc. // to handle NaN properly int opCmp(T other) {You can use: return typeid(T).compare(this, &other); But you've still got the NaN issue..} }
May 08 2007
Jari-Matti Mäkelä Wrote:
Let's say I want to write a wrapper around a primitive type (it could
possibly also be a class or struct, but that isn't necessary now). What's
the best way to do opCmp? I've seen there is TypeInfo.compare there
somewhere, but how does it work? I get
Error: this for compare needs to be type TypeInfo not type Foo *
Also, if it works, does it have performance problems? I read from the ng
archives that the compiler might not inline it.
Here's the stuff I'm writing:
struct Foo(T) {
T value;
// or maybe T opCmp(T other) for reals, floats etc.
// to handle NaN properly
int opCmp(T other) {
// I would like to do something like
// return builtin.opCmp(value, other.value);
// because there are so many special cases for
// the primitive types and it feels a bit stupid
// to reimplement the comparison in every wrapper
}
}
You could probably cast to a void[] and opcmp that. Depends on whether you want
to compare by value or by pointer.
This should work:
int opCmp!(T)(T o1, T o2) {
return ((*(cast(void[]*)(cast(void*)o1)))==(*(cast(void[]*)(cast(void*)o2))));
}
It should work for any type, primitive or otherwise.
May 08 2007