builder.cs

    public class Demo
    {
        public static void DemoIt()
        {
            var builder = new GenericBuilder<TypeTrue, TypeFalse>();
            // builder.Build(); Not valid

            var builder2 = new GenericBuilder<TypeTrue, TypeTrue>();
            builder2.Build();
        }
    }

    public interface ITypeBool { }

    public class TypeTrue : ITypeBool { }
    public class TypeFalse : ITypeBool { }

    public class GenericBuilder<TA, TB>
    {

    }

    public static class Ext
    {
        public static void Build<TA, TB>(this GenericBuilder<TA, TB> builder)
            where TA: TypeTrue
            where TB: TypeTrue
        {
        }
    }