TypeConverter cannot convert from some base types to same base types

Question

Why those return true:

  TypeDescriptor.GetConverter(typeof(double)).CanConvertTo(typeof(double));
  TypeDescriptor.GetConverter(typeof(int)).CanConvertTo(typeof(int));

when those return false?

  TypeDescriptor.GetConverter(typeof(decimal)).CanConvertTo(typeof(decimal));
  TypeDescriptor.GetConverter(typeof(bool)).CanConvertTo(typeof(bool));

Event considering that all the converters returned by GetConverter are supposed to only convert the types to and from a string :

• DoubleConverter
• Int32Converter
• DecimalConverter
• BooleanConverter

I'm using .NET Framework 4.5.2.

Answer 1

DecimalConverter (as well as DoubleConverter and Int32Converter) overrides CanConvertTo to indicate it can convert to strings (because that's what base.CanConvertTo does) and all CLR primitive types. From the Reference Source:

public override bool CanConvertTo(ITypeDescriptorContext context, Type t) 
{
    if (base.CanConvertTo(context, t) || t.IsPrimitive) {
        return true;
    }
    return false;
}

decimal is NOT a primitive type from the CLR's perspective, so the converter returns false when passed typeof(decimal).

BooleanConverter does not override CanConvertTo, so it falls to the base implementation which only allows a conversion to string:

public virtual bool CanConvertTo(ITypeDescriptorContext context, Type destinationType) 
{
    return (destinationType == typeof(string));
}

If you're asking why it's designed that way, then only the Framework designers can say, but I suspect it's because it's a trivial check to see if you're trying to convert from one type to the same type.

Considering that their purpose is to convert non-string types to/from strings for displaying in property grids, XAML, etc., it's not surprising that it doesn't fully support non-string conversions.