relationship of dynamic parameter and visibility.

dynamic.cs

using static System.Console;


namespace Playground
{
	public class OuterClass
	{
		public OuterClass(int value) => Value = value;
		public int Value { get; }

		public static bool operator ==(OuterClass x, OuterClass y)
		{
			WriteLine($"{nameof(OuterClass)}.op_Equality is called.");

			return x.Value == y.Value;
		}

		public static bool operator !=(OuterClass x, OuterClass y)
		{
			WriteLine($"{nameof(OuterClass)}.op_Inequality is called.");
			return x.Value == y.Value;
		}
	}

	class Program
	{
		static void Main(string[] args)
		{
			dynamic x = new InnerClass(42);
			dynamic y = new InnerClass(42);

			//InnerClassはUseDynamic.CallOpEqualityViaDynamicから不可視なので、Objectのop_Equalityが呼ばれて、falseになる。
			WriteLine(UseDynamic.CallOpEqualityViaDynamic(x, y));
			WriteLine();

			x = new OuterClass(42);
			y = new OuterClass(42);

			//OuterClassはUseDynamic.CallOpEqualityViaDynamicから可視なので、Outerのop_Equalityが呼ばれて、trueになる。
			WriteLine(x == y);
		}

		private class InnerClass
		{
			public InnerClass(int value) => Value = value;
			public int Value { get; }

			public static bool operator ==(InnerClass x, InnerClass y)
			{
				WriteLine($"{nameof(InnerClass)}.op_Equality is called.");

				return x.Value == y.Value;
			}

			public static bool operator !=(InnerClass x, InnerClass y)
			{
				WriteLine($"{nameof(InnerClass)}.op_Inequality is called.");
				return x.Value == y.Value;
			}
		}
	}

	static class UseDynamic
	{
		public static bool CallOpEqualityViaDynamic(dynamic a, dynamic b) => a == b;
	}
}