How to check if implicit or explicit cast exists?

.net, c#, casting

Solution

Given that you want to convert from the sealed String type, you can ignore possible nullable, boxing, reference and explicit conversions. Only `op_Implicit()` qualifies. A more generic approach is provided by the System.Linq.Expressions.Expression class:

using System.Linq.Expressions;
...
    public static T DoSomethingWith(string s)
    {
      var expr = Expression.Constant(s);
      var convert = Expression.Convert(expr, typeof(T));
      return (T)convert.Method.Invoke(null, new object[] { s });
    }

Beware the cost of Reflection.

Problem

I have a generic class and I want to enforce that instances of the type parameter are always "cast-able" / convertible from String. Is it possible to do this without for example using an interface? Possible implementation: ``` public class MyClass<T> where T : IConvertibleFrom<string>, new() { public T DoSomethingWith(string s) { // ... } } ``` Ideal implementation: ``` public class MyClass<T> { public T DoSomethingWith(string s) { // CanBeConvertedFrom would return true if explicit or implicit cast exists if(!typeof(T).CanBeConvertedFrom(typeof(String)) { throw new Exception(); } // ... } } ``` The reason why I would prefer this "ideal" implementation is mainly in order not to force all the Ts to implement IConvertibleFrom<>.

Original source