Why it is not possible to define generic indexers in .NET?

Question

Why can\'t you create a generic indexer in .NET?

the following code throws a compiler error:

   public T this[string key]
   {
      get { /         


        

Answer 1

Here's a place where this would be useful. Say you have a strongly-typed OptionKey for declaring options.

public static class DefaultOptions
{
    public static OptionKey SomeBooleanOption { get; }
    public static OptionKey SomeIntegerOption { get; }
}

Where options are exposed through the IOptions interface:

public interface IOptions
{
    /* since options have a default value that can be returned if nothing's
     * been set for the key, it'd be nice to use the property instead of the
     * pair of methods.
     */
    T this[OptionKey key]
    {
        get;
        set;
    }

    T GetOptionValue(OptionKey key);
    void SetOptionValue(OptionKey key, T value);
}

Code could then use the generic indexer as a nice strongly-typed options store:

void Foo()
{
    IOptions o = ...;
    o[DefaultOptions.SomeBooleanOption] = true;
    int integerValue = o[DefaultOptions.SomeIntegerOption];
}