Refactoring if-else if - else

Question

I have the following code example

if(object.Time > 0 && <= 499)
{
     rate = .75m
}
else if(object.Time >= 500 && <= 999)
{
     rate = .85m
}
else if(object.Time >= 1000)
{
     rate = 1.00m
}
else
{
     rate = 0m;
}

My question is what design pattern can I use to make this better?

Edit: Just to clarify a little better, the code you see here is something that currently exists within a Strategy Pattern Implementation. We have 3 types of calculations 2 of which has 3 different "rates" that could be used based off of the time you see below. I thought about creating a strategy implementation for each rate, but then I would be moving the logic for determining the strategy to use and make that a mess as well.

Thanks!

Answer 1

If you're really looking for a design pattern, I'd go for the Chain of Responsibility pattern.

Basically your "link" tries to handle the input. If it is unable to handle it, it's passed down the chain until an other link can handle it. You can also define an interface for easy mocking in your unit tests, if you have some.

So you have this abstract class that every link will inherit :

public abstract class Link
{
    private Link nextLink;

    public void SetSuccessor(Link next)
    {
        nextLink = next;
    }

    public virtual decimal Execute(int time)
    {
        if (nextLink != null)
        {
            return nextLink.Execute(time);
        }
        return 0;
    }
}

And then you create each links with your rules :

public class FirstLink : Link
{
    public override decimal Execute(int time)
    {
        if (time > 0 && time <= 499)
        {
            return .75m;
        }

        return base.Execute(time);
    }
}

public class SecondLink : Link
{
    public override decimal Execute(int time)
    {
        if (time > 500 && time <= 999)
        {
            return .85m;
        }

        return base.Execute(time);
    }
}

public class ThirdLink : Link
{
    public override decimal Execute(int time)
    {
        if (time >= 1000)
        {
            return 1.00m;
        }

        return base.Execute(time);
    }
}

Finally, to use it, just set every successor and call it :

Link chain = new FirstLink();
Link secondLink = new SecondLink();
Link thirdLink = new ThirdLink();


chain.SetSuccessor(secondLink);
secondLink.SetSuccessor(thirdLink);

and all you have to do, is call the chain with one clean call:

var result = chain.Execute(object.Time);