CODEWITHSUNDEEP
c#
zaknotzach
zaknotzach

Reputation: 1005

Better way to deal with is/as checking and casting

All over in our code we type check things, and then immediately need to cast them. Something like this:

if((foo is SomeClass) && (foo as SomeClass).Bar != null) {
    SomeClass fooClass = foo as SomeClass;
    DoSomething(fooClass.Bar);
    ...
}

What I wish is that there was some way that, after an explicit type check, references to foo could implicitly be converted to the class:

if (foo is SomeClass && foo.Bar != null) {
    DoSomething(foo.Bar);
}

It passed (foo is SomeClass) so we know that foo is a SomeClass. The as cast seems superfluous. If you're inside a statement where you have passed (foo is SomeClass) then it seems like you shouldn't have to then explicitly convert foo to SomeClass

Before anyone says anything about coding practices... I know. Ideally in most places in our application we make good use of generics, abstract classes, interfaces, and all other methods to interact with objects in a reasonable manner. But sometimes you get an object and need to check it, especially out of things like events. I don't have a real problem with doing is/as all over, I was just curious if there was some syntactical magic I could employ that was a bit cleaner. This is an experiment in syntax optimization, not practicality.

As a test, I played with an extension method called I called IsAs:

public static bool IsAs<T>(this object check, out T result) {
    if (check is T) {
        result = (T)check;
        return true;
    }
    result = default(T);
    return false;
}

This returns a bool, fulfilling the is portion, and uses a reference input to populate the cast value for the as. But in practice, the syntax is not much cleaner:

SomeClass fooClass;
if(foo.IsAs<SomeClass>(out fooClass) && fooClass.Bar != null) {
    DoSomething(fooClass)
    ...
}

Upvotes: 2

Views: 79

Answers (1)

Noah Stahl
Noah Stahl

Reputation: 7553

Using an is type pattern expression, you can assign the resulting cast to a variable:

if (foo is SomeClass fooSomeClass && fooSomeClass.Bar != null) 
{
    DoSomething(fooSomeClass.Bar);
}

Upvotes: 10

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