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

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?

CodePudding user response：

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

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

The same approach can be used for other similar opeartions.

For build in support - monitor this github issue.