CODEWITHSUNDEEP
c#genericscasting
Thomas Eding
Thomas Eding

Reputation: 1

Circumvent type system for casting a generic type

C# won't let me cast a type T to a type I can prove T to be. How can I cast T to that type?

public static T _cast<T> (object o) {
    if (typeof(T) == typeof(string)) {
        return (T) o.ToString(); // Compiler YELLS!
    }
    throw new InvalidCastException("missing compiler generated case");
}

I'm writing a program that generates code from C++ to C#. This _cast operation I want to use in place of C++'s operator T ().

Upvotes: 1

Views: 134

Answers (4)

Gaute L&#248;ken
Gaute L&#248;ken

Reputation: 7892

I think a more elegant solution than your double cast is using the as keyword. Like this:

return o.ToString() as T;

I didn't try it, but the compiler shouldn't have an issue with that since it will return null when it can't cast the string to T, which within your conditional it won't do of course.

Upvotes: 3

cordialgerm
cordialgerm

Reputation: 8503

There's a difference between casting and parsing. I think what you want is to try and parse strings

int stringToNum = (int)"123";  //will not compile

int stringToNum2 = int.Parse("123");

Upvotes: 0

Thomas Eding
Thomas Eding

Reputation: 1

Normally I don't answer my own questions, but I just came up with the solution: downcast to object before casting to T

public static T _cast<T> (object o) {
    if (typeof(T) == typeof(string)) {
        return (T)(object) o.ToString();
    }
    throw new InvalidCastException("missing compiler generated case");

}

Upvotes: 3

Peter Ritchie
Peter Ritchie

Reputation: 35870

There is no conversion from String to every other type. The compiler is telling you it doesn't know how to do what you've asked. If you provide more detail about what you're trying to do, maybe someone can offer some advice.

Upvotes: 0

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