c# - 完整.NET Framework和.NET Core之间的lambda表达式差异

Question

.NET Framework和.NET Core之间的lambda表达式声明之间有区别吗？
以下表达式在.NET Core中进行编译:

var lastShift = timeline.Appointments
                        .OfType<DriverShiftAppointment>()
                        .SelectMany(x => x.Activities.Where(x => !x.IsTheoretical))
                        .OrderByDescending(x => x.Start)
                        .FirstOrDefault();

但是不在.NET框架中。
此表达式中的问题是以下部分

.SelectMany(x => x.Activities.Where(x => !x.IsTheoretical))

其中 x声明了两次( SelectMany和 Where)。
这是.NET Framework中的错误:

A local or parameter named 'x' cannot be declared in this scope because that name is used in an enclosing local scope to define a local or parameter

.NET框架

可重现的示例:

public class DemoClass
{
    public IList<int> Numbers { get; set; } = new List<int>();
}

class Program
{
    static void Main(string[] args)
    {
        var lst = new List<DemoClass>
        {
            new DemoClass
            {
                Numbers = new List<int>{ 1, 2, 3, 4, 5, 6, 7, 8 }
            },
            new DemoClass
            {
                Numbers = new List<int>{ 1, 2, 3, 4, 5, 6, 7, 8 }
            },
            new DemoClass
            {
                Numbers = new List<int>{ 1, 2, 3, 4, 5, 6, 7, 8 }
            }
        };

        var result = lst.SelectMany(x => x.Numbers.Where(x => x % 2 == 0))
                        .OrderByDescending(x => x);

        Console.WriteLine("Hello World!");
    }
}

Answer 1

它告诉您问题是此行:

.SelectMany(x => x.Activities.Where(x => !x.IsTheoretical))

两次使用x会使它混淆，这是不明确的，请尝试以下操作:

.SelectMany(x => x.Activities.Where(y => !y.IsTheoretical))

但是您是对的，它在核心而不是框架中进行编译。看起来像这样: https://github.com/dotnet/roslyn/issues/38377。阅读该链接，看起来这是C#8.0中的更改，核心目标是8.0，而框架目标是7.2。