Linq method Sum not supported in .NET 7 generic math?

Question

I have the following code, but it does not compile in Visual Studio 17.4 preview 2.1 and .NET 7 RC1 SDK:

using System.Numerics;

int averageInt = Average<int, int>(1, 5, 10);
Console.WriteLine(averageInt);

double averageDouble = Average<int, double>(1, 5, 10);
Console.WriteLine(averageDouble);

TResult Average<TInput, TResult>(params TInput[] numbers)
    where TInput : INumber<TInput>
    where TResult : INumber<TResult> => numbers.Sum() / TResult.CreateChecked(numbers.Length);

The compiler error I get is: Error CS1929 'TInput[]' does not contain a definition for 'Sum' and the best extension method overload 'Queryable.Sum(IQueryable<decimal>)' requires a receiver of type 'IQueryable<decimal>'

I tried the following as an alternative, but it also doesn't compile:

using System.Numerics;

int averageInt = Average<int, int>(1, 5, 10);
Console.WriteLine(averageInt);

double averageDouble = Average<int, double>(1, 5, 10);
Console.WriteLine(averageDouble);

TResult Average<TInput, TResult>(params TInput[] numbers)
    where TInput : INumber<TInput>
    where TResult : INumber<TResult> => numbers.AsQueryable().Sum() / TResult.CreateChecked(numbers.Length);

With the error: Error CS1929 'IQueryable<TInput>' does not contain a definition for 'Sum' and the best extension method overload 'Queryable.Sum(IQueryable<decimal>)' requires a receiver of type 'IQueryable<decimal>'

What am I missing here?

Answer 1

ATM there is no overload for Enumerable.Sum (as for Max, Min etc.) leveraging the generic math. For now you can work around using Enumerable.Aggregate:

TResult Average<TInput, TResult>(params TInput[] numbers)
    where TInput : INumber<TInput>
    where TResult : INumber<TResult> 
    => numbers.Aggregate(TResult.Zero, (agg, t) => agg + TResult.CreateChecked(t)) 
          / TResult.CreateChecked(numbers.Length);

The same approach can be used for other similar operations.

For build in support - monitor this github issue.