ConfigurationExtensions.Get<T>() should support TypeConverters

[Kieranties]

The current implementation uses Convert.ChangeType which only handles types that implement IConvertible.

A small change to allow the use of TypeConverters would improve mapping values to other types.

e.g.

#if NET45 || ASPNET50 || ASPNETCORE50
        public static T Get<T>(this IConfiguration configuration, string key)
        {
            var type = typeof(T);
            var value = configuration.Get(key);
#if ASPNETCORE50            
            return (T)Convert.ChangeType(value, type);
#elif NET45 || ASPNET50
            if (typeof(IConvertible).IsAssignableFrom(type))
            {
                return (T)Convert.ChangeType(value, type);
            }
            else
            {
                var converter = TypeDescriptor.GetConverter(type);
                if (converter == null) throw new InvalidCastException("Could not find a valid TypeConverter for type " + type.FullName);

                return (T)converter.ConvertFromInvariantString(value);
            }
#endif
        }
#endif

[Kieranties]

Hey all, I guess with #199 in place, this can be closed?

Edit: Looks like the ConfigurationBinder has been moved into this project from Options. So the above still applies (but in the ConfigurationBinder class)

[divega]

POCO binding was moved from Options into the Configuration repo recently (see #205). It is currently in Microsoft.Framework.ConfigurationModel although I think it is misplaced there (see #210). Regardless of the specific location, would any part of this improvement apply to the new code?

[Kieranties]

@divega I'd think the logic when using the full runtime could still be applied at https://github.com/aspnet/Configuration/blob/dev/src/Microsoft.Framework.ConfigurationModel/ConfigurationBinder.cs#L217. Essentially, anywhere Convert.ChangeType is used TypeConverters should also be considered.

[HaoK]

This has been done

[HaoK]

3476fad

[Kieranties]

Brilliant!