c# rewrite complex condition check logic using predicates

Question

What is the idea of c# Predicate ? Is it possible to rewrite complex condition check logic using predicates?

private bool HasChanged(object originalValue, object currentValue)
{
    if ((originalValue == null && currentValue != null) || 
        (originalValue != null && !originalValue.Equals(currentValue)))
    {
        return true;
    }
    
    return false;
}

Does this answer your question? [Predicate Delegates in C#](https://stackoverflow.com/questions/556425/predicate-delegates-in-c-sharp) — gunr2171, Jul 14 '22 at 12:20
`Predicate` is essentially just a wrapper for `Func` and can be used to encapsulate code that takes a single value and returns a `bool` result. Take a look at [Delegates: Predicate vs. Action vs. Func](https://stackoverflow.com/questions/566860/delegates-predicate-vs-action-vs-func) for more info — phuzi, Jul 14 '22 at 12:20
See also [What is a predicate in c#?](https://stackoverflow.com/questions/1710301/what-is-a-predicate-in-c) — gunr2171, Jul 14 '22 at 12:21
[Predicate](https://learn.microsoft.com/en-us/dotnet/api/system.predicate-1?view=netframework-2.0) predates, later more generic delegates like [Func](https://learn.microsoft.com/en-us/dotnet/api/system.func-1?view=netframework-3.5) which were introduced with LINQ. — Jodrell, Jul 14 '22 at 12:30

score 3 · Answer 1 · answered Jul 14 '22 at 12:26

Predicate<T> is just a delegate that takes a T and returns bool. It's the equivalent of Func<T, bool> or a method with the signature bool Method<T>(T input).

It doesn't really help you here with your method.

You can, however, simplify your method to this:

private bool HasChanged(object originalValue, object currentValue) =>
    originalValue == null
    ? currentValue != null
    : !originalValue.Equals(currentValue);

score 1 · Answer 2 · answered Jul 14 '22 at 12:27

1

Try this:

bool HasChanged(object originalValue, object currentValue)
    => !(originalValue?.Equals(currentValue) ?? currentValue == null);

answered Jul 14 '22 at 12:27

Petr Voborník

1,249
1
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11

score 0 · Answer 3 · answered Jul 14 '22 at 12:26

You can use a predicate to check on object agains another object declaring the predicate as an object method. Something like

class MyClass
{
    public bool isValid(object obj)
    {
        if (obj is MyClass)
            return true;
        return false;
    }
}

public static class Program
{ 
    static int Main()
    {
        MyClass c1 = new ();

        Predicate<MyClass> predicate = c1.isValid;
        MyClass c2 = new ();
        if (predicate(c2))
        {
            Console.WriteLine("c1 is valid");
        }
        else 
        {
            Console.WriteLine("c1 is not valid");
        }

        return 0;
    }
}

You do realize, that you could simply do `public bool isValid(object obj) => (obj is MyClass);` ? — Fildor, Jul 14 '22 at 12:33
Or even slightly better: `public bool IsValid(object obj) => obj is MyClass;` — Enigmativity, Jul 14 '22 at 12:41

score 0 · Answer 4 · answered Jul 14 '22 at 12:26

You could simplify this a little by flipping the logic and not attempting to cram it in to a single clause

private bool HasChanged(object originalValue, object currentValue)
{
    var bothNull = originalValue == null && currentValue == null;

    if (bothNull){
        return false;
    }

    // at least one of them is not null
    var areSame = originalValue?.Equals(currentValue) ?? false;

    return !areSame;
}

c# rewrite complex condition check logic using predicates

4 Answers4