How do I call my own implementations of interface members?

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I am trying to create a class (Measurement) that should mimic the internal C# numeric classes (int, double, float, etc) as closely as possible. To this end I have defined the Measurement class to have its own implementations of the methods used by the C# classes.

However, I am having trouble accessing the new implementions. The code example below shows the syntax I am using.

My class includes the following in order to define the TryConvertFromChecked() method:

C#

public partial class Measurement<T> : ..., INumberBase<Measurement<T>>,...
        where T : ...,INumberBase<T>, ...
    {
...
        /// <inheritdoc cref="INumberBase{TSelf}.TryConvertFromChecked{TOther}(TOther, out TSelf)" />
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        static bool INumberBase<Measurement<T>>.TryConvertFromChecked<TOther>(TOther value, [MaybeNullWhen(false)] out Measurement<T> result)
        {
            return TryConvertFrom(value, out result, ConversionOption.Checked);
        }

        private static bool TryConvertFrom<TOther>([NotNull] TOther value, [MaybeNullWhen(false)] out Measurement<T> result, ConversionOption option)
            where TOther : INumberBase<TOther>
        {
            ...
        }
...
    }

And I am trying to call that method as follows:

C#

if (!T.TryConvertFromChecked(toUnit.CompoundFactor, out var toCompoundFactor))
    {
        throw new ApplicationException($"An internal error occurred while converting the CompoundFactor for [{unitSymbol}] from type [{toUnit.CompoundFactor}] to type [{typeof(T)}]");
    }

But this is always executing the C# internal System.Numerics.INumberBase<tself> implementation. How would I get my call to TryConvertFromChecked() to call the one that I have created?

What I have tried:

C#

if (!T.Measurement<T>.TryConvertFromChecked(toUnit.CompoundFactor, out var toCompoundFactor))

Results in CS0704 Cannot do non-virtual member lookup in 'T' because it is a type parameter

Posted 9-Feb-24 6:36am

C Pottinger

Updated 9-Feb-24 10:02am

v4

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Comments

[no name] 9-Feb-24 15:45pm

Why? .NET doesn't do generic type conversions. And what are you measuring? What is the "unit of measure". I measure pixels. Then, based on the context, I get back the equivalent in yards, or paces, or inches (based on scaling). As in, Distance.FromYards(x). Or x = Distance.ToPixels().

C Pottinger 9-Feb-24 21:05pm

It seems that .NET does do generic type conversions - at least that is what Systems.Numerics.INumberBase seems to suggest (see https://learn.microsoft.com/en-us/dotnet/api/system.numerics.inumberbase-1.tryconvertfromchecked?view=net-8.0#system-numerics-inumberbase-1-tryconvertfromchecked-1(-0-0@)).
The unit of measurement is not actually pertinent to the problem. I am just trying to find out the proper way to set up and/or call my implementation of TryConvertFromChecked.

[no name] 10-Feb-24 15:08pm

All the system types "derive" from that base (they've done the work for you) ... In that sense it's far removed from List<t>. And you're trying to implement an (apparent) "value" interface on a "class" (yours). You should review the .NET source code for what you're trying to reproduce.

Graeme_Grant 9-Feb-24 19:03pm

This is an issue that is difficult to diagnose here with the information given. I think that i may know what is happening, and want to make sure that I have the right solution before answering.

So, to avoid excess time digging into code, can you create a new project with just one example, not your entire code base, that demonstrates the issue? If you can, update your question with a link and then we can run and see what is happening.

C Pottinger 9-Feb-24 21:06pm

I have created a stripped down program. Stepping through it shows that the call to TryConvertFromChecked() does not call the one defined in the code.

https://drive.google.com/file/d/1J028ZWLARdQo9xlk_RLIs8-WSyQkFMoI/view?usp=sharing

C Pottinger 13-Feb-24 6:55am

Thank you, Graeme. Your analysis matches exactly what I was seeing happen.
Since the conversion cannot be customized, I will have to rethink the idea of applying all the interfaces commonly used by the intrinsic numeric types.
I will look into the TypeConverter class, as you suggested.
And thank you for the link to the .NET source browser - I was not aware of this resource.

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Graeme_Grant · Accepted Answer · 2024-02-09T16:23:00

Here is your problem:

C#

T.TryConvertFromChecked(toUnit.CompoundFactor, out var toCompoundFactor)

This calls the TryConvertFromChecked in the readonly struct Double. Here is the method:

C#

static bool INumberBase<double>.TryConvertFromChecked<TOther>(TOther value, out double result)
{
    return TryConvertFrom<TOther>(value, out result);
}

and the TryConvertFrom:

C#

private static bool TryConvertFrom<TOther>(TOther value, out double result)
    where TOther : INumberBase<TOther>
{
    // In order to reduce overall code duplication and improve the inlinabilty of these
    // methods for the corelib types we have `ConvertFrom` handle the same sign and
    // `ConvertTo` handle the opposite sign. However, since there is an uneven split
    // between signed and unsigned types, the one that handles unsigned will also
    // handle `Decimal`.
    //
    // That is, `ConvertFrom` for `double` will handle the other signed types and
    // `ConvertTo` will handle the unsigned types

    if (typeof(TOther) == typeof(Half))
    {
        Half actualValue = (Half)(object)value;
        result = (double)actualValue;
        return true;
    }
    else if (typeof(TOther) == typeof(short))
    {
        short actualValue = (short)(object)value;
        result = actualValue;
        return true;
    }
    else if (typeof(TOther) == typeof(int))
    {
        int actualValue = (int)(object)value;
        result = actualValue;
        return true;
    }
    else if (typeof(TOther) == typeof(long))
    {
        long actualValue = (long)(object)value;
        result = actualValue;
        return true;
    }
    else if (typeof(TOther) == typeof(Int128))
    {
        Int128 actualValue = (Int128)(object)value;
        result = (double)actualValue;
        return true;
    }
    else if (typeof(TOther) == typeof(nint))
    {
        nint actualValue = (nint)(object)value;
        result = actualValue;
        return true;
    }
    else if (typeof(TOther) == typeof(sbyte))
    {
        sbyte actualValue = (sbyte)(object)value;
        result = actualValue;
        return true;
    }
    else if (typeof(TOther) == typeof(float))
    {
        float actualValue = (float)(object)value;
        result = actualValue;
        return true;
    }
    else
    {
        result = default;
        return false;
    }
}

The conversion is not open for customisation in the manner that you want. you would be better off looking at using the TypeConverter Class (System.ComponentModel) | Microsoft Learn[^]

However, if you still want to go down this route, have a look at .NET Source Browser - BigInteger[^] to see how Microsoft approach it.