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有没有办法声明一个C#lambda并立即调用它?

lambda c#

Glorfindel Doug L. · 技术社区 · 5 年前

Func<int, int> lambda = (input) => { return 1; };
int output = lambda(0);

我想知道是否可以在一行中这样做,例如

int output = (input) => { return 1; }(0);

它给出了一个编译器错误“需要方法名”。铸造到 Func<int, int> 也不起作用:

int output = (Func<int, int>)((input) => { return 1; })(0);

int ).

你可能在想我想这样做,而不是直接嵌入代码。 int output = 1; . 原因如下:我为SOAP webservice生成了一个引用 svcutil

var o = await client.GetOrderAsync(request);
return new Order {
    OrderDate = o.OrderDate,
    ...
    Shipments = o.Shipment_Order == null ? new Shipment[0]
        o.Shipment_Order.Select(sh => new Shipment {
            ShipmentID = sh.ShipmentID,
            ...
            Address = CreateAddress(sh.ReceiverAddress_Shipment);
        }).ToArray()
};

和一个单独的 CreateAddress(GetOrderResultOrderShipment_OrderShipmentShipment_Address address) 方法(实名甚至更长,我对表单的控制非常有限),我想编写

var o = await client.GetOrderAsync(request);
return new Order {
    OrderDate = o.OrderDate,
    ...
    Shipments = o.Shipment_Order == null ? new Shipment[0]
        o.Shipment_Order.Select(sh => new Shipment {
            ShipmentID = sh.ShipmentID,
            ...
            Address = sh.ReceiverAddress_Shipment == null ? null : () => {
                var a = sh.ReceiverAddress_Shipment.Address;
                return new Address {
                    Street = a.Street
                    ...
                };
            }()
        }).ToArray()
};

Address = sh.ReceiverAddress_Shipment == null ? null : new Address {
    Street = sh.ReceiverAddress_Shipment.Address.Street,
    ...
}

但即使如此 sh.ReceiverAddress_Shipment.Address 如果有许多字段,则会变得非常重复。声明一个lambda并立即调用它 ~~更优雅~~

4 回复 | 直到 5 年前

Glorfindel Doug L. 5 年前

我建议您使用一个小的helper函数,而不是尝试转换lambda:

public static TOut Exec<TIn, TOut>(Func<TIn, TOut> func, TIn input) => func(input);

你可以这样使用: int x = Exec(myVar => myVar + 2, 0); . 这对我来说要比这里建议的替代方案好得多。

Johnathan Barclay 5 年前

很难看,但有可能:

int output = ((Func<int>)(() => { return 1; }))();

可以强制转换,但lambda需要括在括号中。

以上也可以简化:

int output = ((Func<int>)(() => 1))();

Cyril Durand 5 年前

您还可以在 Select 方法

var o = await client.GetOrderAsync(request);
return new Order {
    OrderDate = o.OrderDate,
    ...
    Shipments = o.Shipment_Order == null ? new Shipment[0]
        o.Shipment_Order.Select(sh => {
          var s = sh.ReceiverAddress_Shipment;
          var a = s.Address;
          return new Shipment {
            ShipmentID = sh.ShipmentID,
            ...
            Address = s == null ? 
                      null : 
                      new Address {
                        Street = a.Street
                        ...
                      }
          };
        }).ToArray()
};

?? 操作人员

var o = await client.GetOrderAsync(request);
return new Order {
    OrderDate = o.OrderDate,
    ...
    Shipments = o.Shipment_Order?.Select(sh => {
        var s = sh.ReceiverAddress_Shipment;
        var a = s.Address;
        return new Shipment {
            ShipmentID = sh.ShipmentID,
            ...
            Address = s == null ? 
                      null : 
                      new Address {
                          Street = a.Street
                          ...
                      }
        };
    }).ToArray() ?? new Shipment[0]
};

Glorfindel Doug L. 5 年前

您可以内联 Func

int output = (new Func<int, int>(() => { return 1; }))(0);

立即调用它。