Visual Studio 2017 Compiler Error(s)

Question

I just upgraded to VS2017 but right off the bat my project can no longer be built, as I am getting a bunch of strange compiler errors that didn't exist when I was using VS15.

Errors such as:

• Syntax Error; value expected
• Invalid Expression Term '['
• Invalid Expression Term 'byte'
• Using the generic type requires 1 type arguments

Edit 1:

• Just created a small Console App and copied some of the code to it and the same compiler error(s) appeared

using System;
using System.Runtime.InteropServices;

namespace Error
{
    class Program
    {
        static void Main()
        {
            Array array2D = null;
            if (array2D is Bgra <byte>[,])
            {
            }
        }
    }

    public interface IColor { }

    public interface IColor<T> : IColor
        where T : struct
    { }

    public interface IColor2 : IColor { }

    public interface IColor2<T> : IColor2, IColor<T>
        where T : struct
    { }

    public interface IColor3 : IColor { }

    public interface IColor3<T> : IColor3, IColor<T>
        where T : struct
    { }

    public interface IColor4 : IColor { }

    public interface IColor4<T> : IColor4, IColor<T>
        where T : struct
    { }

    [StructLayout(LayoutKind.Sequential)]
    public struct Bgra<T> : IColor4<T>
        where T : struct
    {
        public Bgra(T b, T g, T r, T a)
        {
            B = b;
            G = g;
            R = r;
            A = a;
        }

        public T B;

        public T G;

        public T R;

        public T A;

        public override string ToString()
        {
            return $"B: {B}, G: {G}, R: {R}, A: {A}";
        }

        public const int IDX_B = 0;

        public const int IDX_G = 1;

        public const int IDX_R = 2;

        public const int IDX_A = 3;
    }
}

Note that the exact same project compiles okay in VS15 and even VS13.

Edit 2:

• VS15 <=> VS17

Answer 1

According to my test, using as operator works as expected in Visual Studio 2017.

So you can use

var tmp = array2D as Bgra<Byte>[,]; 
if (tmp != null) { ... }

Also, is operator do works with simple array :

if (array2D is int[,]) { ... }

would also compile.

So it seems that the problematic case if when you have an array of generics. In fact, if you do something like

if (array2D is List<int>[,]) { ... }

you would get the compilation error.

Also the following code would compile

object something = null;
if (something is List<int>) { ... }

Thus, the only problematic case is when using an array of a generic type as the argument of the is operator.

As a side note, I would generally prefer using as operator to is operator since usually you need a variable in the target type anyway.

Answer 2

C#7 extends the is operator from pure type testing to what they call Pattern Matching.

The parser now seems to get confused by is followed by array-of-generic. I'd try with parens around the type, but I cannot test this solution

if (array2D is (Bgra<byte>[,]))