• Mandeep Singh Brar (58/58) Jan 27 2011 Hi,
• Jonathan M Davis (12/86) Jan 27 2011 Well, of course the first version doesn't work. opCmp is supposed to ret...
• Steven Schveighoffer (8/13) Jan 28 2011 std.algorithm.sort is a template, so it has access to the fully derived ...

Mandeep Singh Brar <mandeep brars.co.in> writes:

Hi,

I am facing the following problems with sorting. .

module testSort;

import std.stdio;
import std.algorithm;

class testcl {
	public string name;
	this(string na) { name=na; }
	public string toString() {
		return name;
	}
	public int opCmp(testcl b) {

		return name < b.name ?  -1: 1;
	}

}

int main(string[] args) {
	testcl a = new testcl(args[1]);
	testcl b = new testcl(args[2]);
	testcl[] arr = [a,b];
	writeln(arr);
	sort!("a>b")(arr);
	writeln(arr);
	return 0;
}

I get the following input when i run this program as:

./testSort te2 test2
[te2, test2]
[test2, te2]


./testSort test1 test2
[test1, test2]
[test2, test1]

which is as desired.. But randomly with a few strings it gives me a range
violation as:


./testSort test2 te1
[test2, te1]
core.exception.RangeError std.algorithm(5293): Range violation
----------------
./testSort() [0x80599d6]
./testSort() [0x8050ca6]
./testSort() [0x8052b26]
./testSort() [0x804d39d]
./testSort() [0x804d2a8]
./testSort() [0x804ce3a]
./testSort() [0x8049919]
./testSort() [0x8050e66]
./testSort() [0x8050dc0]
./testSort() [0x8050eaa]
./testSort() [0x8050dc0]
./testSort() [0x8050d66]
/lib/libc.so.6(__libc_start_main+0xe7) [0x139ce7]
./testSort() [0x8049751]

The problem gets corrected if i write the comparison function as :

	public int opCmp(testcl b) {
		if(name == b.name) return 0;
		return name < b.name ?  -1: 1;
	}

I could not get the problem with the above code.

Thanks
Mandeep

Jonathan M Davis <jmdavisProg gmx.com> writes:

On Thursday 27 January 2011 20:30:47 Mandeep Singh Brar wrote:
 Hi,
 
 I am facing the following problems with sorting. .
 
 module testSort;
 
 import std.stdio;
 import std.algorithm;
 
 class testcl {
 	public string name;
 	this(string na) { name=na; }
 	public string toString() {
 		return name;
 	}
 	public int opCmp(testcl b) {
 
 		return name < b.name ?  -1: 1;
 	}
 
 }
 
 int main(string[] args) {
 	testcl a = new testcl(args[1]);
 	testcl b = new testcl(args[2]);
 	testcl[] arr = [a,b];
 	writeln(arr);
 	sort!("a>b")(arr);
 	writeln(arr);
 	return 0;
 }
 
 I get the following input when i run this program as:
 
 ./testSort te2 test2
 [te2, test2]
 [test2, te2]
 
 
 ./testSort test1 test2
 [test1, test2]
 [test2, test1]
 
 which is as desired.. But randomly with a few strings it gives me a range
 violation as:
 
 
 ./testSort test2 te1
 [test2, te1]
 core.exception.RangeError std.algorithm(5293): Range violation
 ----------------
 ./testSort() [0x80599d6]
 ./testSort() [0x8050ca6]
 ./testSort() [0x8052b26]
 ./testSort() [0x804d39d]
 ./testSort() [0x804d2a8]
 ./testSort() [0x804ce3a]
 ./testSort() [0x8049919]
 ./testSort() [0x8050e66]
 ./testSort() [0x8050dc0]
 ./testSort() [0x8050eaa]
 ./testSort() [0x8050dc0]
 ./testSort() [0x8050d66]
 /lib/libc.so.6(__libc_start_main+0xe7) [0x139ce7]
 ./testSort() [0x8049751]
 
 The problem gets corrected if i write the comparison function as :
 
 	public int opCmp(testcl b) {
 		if(name == b.name) return 0;
 		return name < b.name ?  -1: 1;
 	}
 
 I could not get the problem with the above code.

Well, of course the first version doesn't work. opCmp is supposed to return 0
if 
the values are equal, and it doesn't do that. opCmp returns a value < 0 if the 
first value is less than the second, 0 if they're equal, and a value > 0 if the 
first value is greater than the second value.

Also, the signature for opCmp on classes is supposed to be

int opCmp(Object o)

It's supposed to take Object. I'm surprised that it works at all the way that
it 
is.

And since you're comparing strings, your opCmp can just use std.string.cmp to 
compare them.

- Jonathan M Davis

"Steven Schveighoffer" <schveiguy yahoo.com> writes:

On Fri, 28 Jan 2011 00:05:34 -0500, Jonathan M Davis <jmdavisProg gmx.com>  
wrote:

 Also, the signature for opCmp on classes is supposed to be

 int opCmp(Object o)

 It's supposed to take Object. I'm surprised that it works at all the way  
 that it
 is.

std.algorithm.sort is a template, so it has access to the fully derived  
class type.  The compiler simply rewrites a < b as a.opCmp(b), which calls  
his function if you are using the derived type.

Without defining opCmp as taking object, however, the builtin array sort  
would fail with a hidden function error.

-Steve