Template question

[truegoodwill]

I wanted to create a number of "NanoValue" struct Ids which are a long representation of a value multiplied by 1E9.

So I started with this:

public readonly partial record struct SomeNanoValue(long Value) : IStructId<long>
{
}

Then, I wanted to be able to explicitly convert it to a decimal with named methods (and certainly not an implicit cast).

So I added this interface:

public interface INanoValueConvertsToDecimal : IStructId<long> 
{
  decimal ToDecimal();
  static abstract INanoValueConvertsToDecimal FromDecimal(decimal value);
}

But I just wasn't able to get the static abstract working in a template. In the end I dropped the template idea and put an unsatisfactory default implementation on the interface itself:

public readonly partial record struct SomeNanoValue(long Value) : IStructId<long>, INanoValueConvertsToDecimal<SomeNanoValue>
{
}

public interface INanoValueConvertsToDecimal<T> : IStructId<long> where T : INanoValueConvertsToDecimal<T>, INewable<T, long>
{
  decimal ToDecimal() => Value / 1E9M;
  static T FromDecimal(decimal value) => T.New((long)(value * 1E9M));
}

It's unsatisfactory because I wanted to use

var x = SomeNanoValue.FromDecimal(21M); // doesn't compile
// instead of 
var y = INanoValueConvertsToDecimal<SomeNanoValue>.FromDecimal(21M); // the best I've got :(

[truegoodwill]

ok here's what I've got now. The system doesn't seem to be applying the template to the value id type though:

public readonly partial record struct SomeNanoValue(long Value) : IStructId<long>, INanoValueConvertsToDecimal
{
}

public interface INanoValueConvertsToDecimal
{
}

[TStructId]
file readonly partial record struct TSelf(TValue Value) : INanoValueConvertsToDecimal
{
  public static TSelf FromDecimal(decimal value)
  {
    return new TSelf((TValue)(long)(value * 1E9M));
  }

  public decimal ToDecimal()
  {
    return Value / 1E9M;
  }
}

file readonly partial record struct TValue : INanoValueConvertsToDecimal
{
  public static decimal operator /(TValue left, decimal right) => throw new NotImplementedException();

  public static explicit operator TValue(long value) => throw new NotImplementedException();
}

No partial type declaration that includes this template:

[truegoodwill]

Welp ... I got this working remarkably simply, guess it was beginner error that messed up my first try at a simple solution. Here's how I did it:

public readonly partial record struct SomeNanoValue(long Value) : IStructId<long>, INanoValueConvertsToDecimal
{
}

// this one is based on ulong instead of long
public readonly partial record struct AnotherNanoValue(ulong Value) : IStructId<ulong>, INanoValueConvertsToDecimal
{
}

public interface INanoValueConvertsToDecimal
{
}

// applies itself only to long-based 
[TStructId]
file readonly partial record struct TSelf(long Value) : INanoValueConvertsToDecimal
{
  public static TSelf FromDecimal(decimal value)
  {
    return new TSelf((long)(value * 1E9M));
  }

  public decimal ToDecimal()
  {
    return Value / 1E9M;
  }
}

// applies itself only to ulong-based 
[TStructId]
file readonly partial record struct TSelf(ulong Value) : INanoValueConvertsToDecimal
{
  public static TSelf FromDecimal(decimal value)
  {
    return new TSelf((ulong)(value * 1E9M));
  }

  public decimal ToDecimal()
  {
    return Value / 1E9M;
  }
}

[truegoodwill]

I really like this library. Am just now adding it to a production code base for the first time. Thank you.