C#•2y ago

✅ Specialising a generic method

I've got a generic method that takes a string and uses a TypeConverter to convert it to a specific type. However, when the requested type is bool, I want 0 and 1 to convert to false and true. I was hoping that I'd be able to do this:

private static T? Convert<T>(string input)
{
    if(typeof(T) == typeof(bool))
    {
        return Convert<int>(input) != 0;
    }

    try
    {
        TypeConverter converter = TypeDescriptor.GetConverter(typeof(T));
        return (T?)converter.ConvertFromString(input);
    }
    catch(NotSupportedException)
    {
        return default;
    }
}

private static T? Convert<T>(string input)
{
    if(typeof(T) == typeof(bool))
    {
        return Convert<int>(input) != 0;
    }

    try
    {
        TypeConverter converter = TypeDescriptor.GetConverter(typeof(T));
        return (T?)converter.ConvertFromString(input);
    }
    catch(NotSupportedException)
    {
        return default;
    }
}

However, I get an error on return Convert<int>(input) != 0; as it says "Cannot implicitly convert type 'bool' to 'T'", even though in this case the if statement has ensured that T is bool. How can I get this to work, either by convincing the compiler that T is bool in that situation, or any other way? Thanks

8 Replies

Anton•2y ago

you can cast it to object and then to T as T should also work I think

HughOP•2y ago

as T says: "[CS0413] The type parameter 'T' cannot be used with the 'as' operator because it does not have a class type constraint nor a 'class' constraint" Casting to object then to T seems to work well, though - thanks!

ero•2y ago

that boxes, no?

HughOP•2y ago

boxes?

Thinker•2y ago

I.e. it turns a value type in a reference type

FusedQyou•2y ago

Manually parse the string "0" or "1" to "false" or "true" before the logic happends? Not the prettiest way, but it gets your fix

Anton•2y ago

I think the boxing there gets optimized out

HughOP•2y ago

Thanks all - very helpful

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✅ Specialising a generic method