2

I do not remember how to do in C# a comparison of a class against a primitive type.

Example

public class Validate{
... //This is here that we would need to add code 
    //if I remember to make the object act as a boolean for example
}

...

Validate v = new Validate(...);
if(v==true)
{
...
}

Do you know the name of that and how to do it?

Patrick Desjardins
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  • possible duplicate of [C# Custom Object Validation Design](http://stackoverflow.com/questions/1290251/c-custom-object-validation-design) – Filip Ekberg Jan 16 '11 at 00:30
  • what behavior are you expecting? Do you want to be able to control that yourself? I mean, do you want v to be true when there is an object, or when it suits your criterias? – Filip Ekberg Jan 16 '11 at 00:31
  • I want that v be compared to True/False. I do not want to use property or method... – Patrick Desjardins Jan 16 '11 at 00:34
  • Yes, but what do you expect True/False to represent? An object that exists might have faulty values, is it still "true" then? – Filip Ekberg Jan 16 '11 at 00:35

4 Answers4

2

I think you're looking for an implicit type conversion.

Add the following method to your Validate class:

    public static implicit operator bool(Validate v)
    {
        // Logic to determine if v is true or false
        return true;
    }
newdayrising
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  • Exactly what I want! Thank you sir! – Patrick Desjardins Jan 16 '11 at 00:40
  • @Daok, I do not think this is exactly what you want. Don’t use an implicit operator unless you can meaningfully and reliably map all possible values of `Validate` to a value of `bool`. If you just want to do `== true` and `== false`, then I recommend the operator overload solution provided by *hunter* below. – Timwi Jan 16 '11 at 05:45
2

To do what you want, you need to override the implicit cast operator:

public class MyObject
{
    private int i;

    public MyObject(int i)
    {
        this.i = i;
    }

    public static implicit operator bool(MyObject o)
    {
        return o.i % 2 == 0;
    }
}

The above example will evaluate to true if the field i is even:

MyObject o1 = new MyObject(1);
MyObject o2 = new MyObject(2);

if (o1)
{
    Console.WriteLine("o1");
}

if (o2)
{
    Console.WriteLine("o2");
}

The output of the above is o2.

However, it is a bit of a horrible implementation as it leads to confusing code in that you have constructs that read as if (object), which would be unfamiliar to most readers - if (object.IsValid) makes the intention much more clearer.

adrianbanks
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1

do you mean operator overloading?

public static bool operator == (Validate v, bool value) 
{
    return /* some comparison */
    // or going off of the other posters answer
    return v.IsValid == value; 
}
hunter
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1

Just add an IsValid property to your Validate class and call that property:

public class Validate
{
    public bool IsValid
    {
        get { [implementation here] }
    }
}

...

Validate v = new Validate(...);
if(v.IsValid)
{
    ...
}

It is possible to create an implicit operator, but it is not advisable to use it this way, because it would make your code hard to follow for other developers.

UPDATE

Okay, just for completeness and education, this is how to do it:

public class Validate
{
    public bool IsValid
    {
        get { [implementation here] }
    }

    public static implicit operator bool(Validate v)
    {
        return v.IsValid;
    }
}

But again, don't do it. It would make your code pretty hard to follow.

Steven
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  • That doesn't allow you to do `v == true` does it? – Filip Ekberg Jan 16 '11 at 00:31
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    @Filip: Nope, and I consider that a good thing. If that really is what the OP wants, he should implement a `public static implicit operator bool(Validate v)` method on the `Validate` type. – Steven Jan 16 '11 at 00:33
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    @Daok: I know you don't want that, but please don't do it. – Steven Jan 16 '11 at 00:34