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digitalmars.D.learn - How to using opCmp

reply Heromyth <bitworld qq.com> writes:
I have defined a opCmp function to overload comparison operators, then how can
I use it correctly?

I can use it like this:
   int b = t1.opCmp(info);
and is it right like this:
   int b = t1 < info;

In my test code, I get different value for b. What can I do?
Thanks for helps.

//=============
//Test code:
//=============
import std.stdio;
import std.conv;
import std.file;
import std.algorithm;
import std.range;
import std.array;
import std.format;
import std.path;
import std.ascii;
import std.utf;
import std.process;

public final class LogLevel
{
     property public static LogLevel Trace()
    {
        if( m_Trace is null )
            m_Trace = new LogLevel("Trace", 0);
        return m_Trace;
    }
    private static LogLevel m_Trace;

     property public static LogLevel Info()
    {
        if( m_Info is null )
            m_Info = new LogLevel("Info", 2);
        return m_Info;
    }
    private static LogLevel m_Info;


    public string getName()
    {
        return name;

    }

    private int ordinal;
    private string name;

    public static LogLevel FromString(string levelName)
    {
        if (levelName.empty())
        {
            throw new Exception("levelName");
        }

        return Trace;
    }

	public  int  opCmp(LogLevel level1)
	{
		int result = 0;
		if( this.Ordinal > level1.Ordinal)
			result = 1;
		else if( this.Ordinal == level1.Ordinal)
			result = 0;
		else
			result = -1;
		writefln("result == %d", result);
		return result;
	}

     property package int Ordinal()
    {
        return this.ordinal;
    }


    private this(string name, int ordinal)
    {
        this.name = name;
        this.ordinal = ordinal;
    }
}


int main(string[] args)
{
    LogLevel t1 = LogLevel.Trace;
    LogLevel t2 = LogLevel.Trace;
    LogLevel info = LogLevel.Info;
	int a = t1 > t2;
	writefln("a == %d", a);

	int b = t1.opCmp(info);
	writefln("b == %d", b);

	b = t1 < info;
	writefln("b == %d", b);

	b = t1 > info;
	writefln("b == %d", b);

    return 0;
}
//=============
Dec 17 2011
next sibling parent reply bearophile <bearophileHUGS lycos.com> writes:
Heromyth:

 I have defined a opCmp function to overload comparison operators, then how can
 I use it correctly?

I don't have an answer yet, but I suggest you to look at the D docs that describe how to use opCmp. Probably you need to accept a const Object, and to use override. I suggest to strip your code from all the not essential things, so you will see the problems better. Bye, bearophile
Dec 17 2011
parent Heromyth <bitworld qq.com> writes:
== Quote from bearophile (bearophileHUGS lycos.com)'s article
 Heromyth:
 I have defined a opCmp function to overload comparison operators, then how can
 I use it correctly?


override. I suggest to strip your code from all the not essential things, so you will see the problems better.
 Bye,
 bearophile

I tested public override int opCmp(Object o) and got the same result. The D document suggests rewriting a < b into a.opCmp(b) < 0 While doing code porting from C# to D, I wander if I can directly use the comparing operation between two class object. Maybe the compiler should give some messages for not using "a < b". Is it a compiler bug? Can anyone give some suggertion. It will be well grateful.
Dec 17 2011
prev sibling next sibling parent "Manfred_Nowak" <svv1999 hotmail.com> writes:
Heromyth wrote:

 I can use it like this:
    int b = t1.opCmp(info);
 and is it right like this:
    int b = t1 < info;
 
 In my test code, I get different value for b. What can I do?

Nothing because the call of the operator `<' interprets the result of the call of `opCmp', which is constant in this case! Remember that the result of `opCmp' is used for at least the operators `<', `>', `<=' and `>='. -manfred
Dec 17 2011
prev sibling parent reply Jesse Phillips <jessekphillips+d gmail.com> writes:
On Sat, 17 Dec 2011 14:06:48 +0000, Heromyth wrote:

 I have defined a opCmp function to overload comparison operators, then
 how can I use it correctly?
 
 I can use it like this:
    int b = t1.opCmp(info);
 and is it right like this:
    int b = t1 < info;

Consider the code more to the point of: int b = t1.opCmp(info); bool c = t1 < info;
Dec 17 2011
parent Heromyth <bitworld qq.com> writes:
== Quote from Jesse Phillips (jessekphillips+d gmail.com)'s article
 On Sat, 17 Dec 2011 14:06:48 +0000, Heromyth wrote:
 I have defined a opCmp function to overload comparison operators, then
 how can I use it correctly?

 I can use it like this:
    int b = t1.opCmp(info);
 and is it right like this:
    int b = t1 < info;

int b = t1.opCmp(info); bool c = t1 < info;

Here is the modified test code: // Test.d import std.stdio; import std.algorithm; import std.range; import std.array; public class LogLevel { property public static LogLevel Trace() { if( m_Trace is null ) m_Trace = new LogLevel("Trace", 0); return m_Trace; } private static LogLevel m_Trace; property public static LogLevel Info() { if( m_Info is null ) m_Info = new LogLevel("Info", 2); return m_Info; } private static LogLevel m_Info; private int ordinal; private string name; public override int opCmp(Object o) { LogLevel level1 = cast(LogLevel) o; int result = 0; if( this.Ordinal > level1.Ordinal) result = 1; else result = -1; writefln("result == %d", result); return result; } property package int Ordinal() { return this.ordinal; } private this(string name, int ordinal) { this.name = name; this.ordinal = ordinal; } } int main(string[] args) { LogLevel t1 = LogLevel.Trace; LogLevel t2 = LogLevel.Trace; LogLevel info = LogLevel.Info; bool a = t1 == t2; writefln("a == %s", a); int b = t1.opCmp(info); writefln("b == %d", b); b = t1 < info; writefln("b == %d", b); bool c = t1 > info; writefln("c == %s", c); c = t1 < info; writefln("c == %s", c); return 0; } /* a == true result == -1 b == -1 result == -1 b == 1 result == -1 c == false result == -1 c == true */
Dec 17 2011