在C#中具有块等效性?
我了解VB.Net,正在努力复习我的C。在C#中是否有与块等效的块在C#中具有块等效性?,c#,.net,vb.net,C#,.net,Vb.net,我了解VB.Net,正在努力复习我的C。在C#中是否有与块等效的块 谢谢不,没有。您可以使用参数累加器模式 关于这一点的大讨论如下: 嗯。我从未深入使用过VB.net,所以我在这里做一个假设,但我认为“使用”块可能接近您想要的 使用定义变量的块范围,请参见下面的示例 using ( int temp = someFunction(param1) ) { temp++; // this works fine } temp++; // this blows up as temp is ou
谢谢不,没有。您可以使用参数累加器模式 关于这一点的大讨论如下:
嗯。我从未深入使用过VB.net,所以我在这里做一个假设,但我认为“使用”块可能接近您想要的 使用定义变量的块范围,请参见下面的示例
using ( int temp = someFunction(param1) ) {
temp++; // this works fine
}
temp++; // this blows up as temp is out of scope here and has been disposed
编辑:是的,这个答案是错误的——最初的假设是错误的。VB的“WITH”更像是新的C#对象初始化器:
var yourVariable = new yourObject { param1 = 20, param2 = "some string" };
大约3/4页下方的“”部分: VB: C#: 虽然C#在一般情况下没有任何直接等价物,但C#3为构造函数调用获得对象初始值设定项语法:
var foo = new Foo { Property1 = value1, Property2 = value2, etc };
有关更多详细信息,请参阅C#Depth的第8章-您可以从免费下载
(免责声明-是的,让更多人掌握这本书符合我的利益。但是,嘿,这是一个免费的章节,为您提供有关相关主题的更多信息…这是Visual C#程序经理必须说的:
许多人,包括C语言设计师,相信“with”
通常会损害可读性,与其说是福,不如说是祸。它是
更清楚地声明具有有意义名称的局部变量,并使用
该变量用于对单个对象执行多个操作,而不是
它是一个具有某种隐式上下文的块
正如上面链接的Visual C#Program Manager所说,在有限的情况下,With语句的效率更高,他举了一个例子,当With语句被用作速记以重复访问复杂表达式时
使用扩展方法和泛型,您可以通过添加以下内容来创建与With语句模糊等效的内容:
public static T With<T>(this T item, Action<T> action)
{
action(item);
return item;
}
为此:
updateRoleFamily.With(rf =>
{
rf.RoleFamilyDescription = roleFamilyDescription;
rf.RoleFamilyCode = roleFamilyCode;
});
在这样一个示例中,唯一的优势可能是更好的布局,但如果有更复杂的引用和更多的属性,它很可能会为您提供更可读的代码。有时您可以通过执行以下操作来避免:
var fill = cell.Style.Fill;
fill.PatternType = ExcelFillStyle.Solid;
fill.BackgroundColor.SetColor(Color.Gray);
fill.PatternColor = Color.Black;
fill.Gradient = ...
(EPPLus@的代码示例)我是这样使用的:
worksheet.get_Range(11, 1, 11, 41)
.SetHeadFontStyle()
.SetHeadFillStyle(45)
.SetBorders(
XlBorderWeight.xlMedium
, XlBorderWeight.xlThick
, XlBorderWeight.xlMedium
, XlBorderWeight.xlThick)
;
SetHeadFontStyle/SetHeadFillStyle是范围的ExtMethod,如下所示:
public static Range SetHeadFillStyle(this Range rng, int colorIndex)
{
//do some operation
return rng;
}
执行一些操作并返回下一个操作的范围
它看起来像Linq:)
但现在仍然不能完全像它--属性集值
with cell.Border(xlEdgeTop)
.LineStyle = xlContinuous
.Weight = xlMedium
.ColorIndex = xlAutomatic
最简单的语法是:
{
var where = new MyObject();
where.property = "xxx";
where.SomeFunction("yyy");
}
{
var where = new MyObject();
where.property = "zzz";
where.SomeFunction("uuu");
}
实际上,如果您想重用变量名,像这样的额外代码块非常方便 如果存在多个级别的对象,您可以通过“使用”指令获得类似的功能:
using System;
using GenderType = Hero.GenderType; //This is the shorthand using directive
public partial class Test : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
var myHero = new Hero();
myHero.Name = "SpamMan";
myHero.PowerLevel = 3;
myHero.Gender = GenderType.Male; //instead of myHero.Gender = Hero.GenderType.Male;
}
}
public class Hero
{
public enum GenderType
{
Male,
Female,
Other
}
public string Name;
public int PowerLevel;
public GenderType Gender;
}
还有另一个有趣的with模式实现
public static T With<T>(this T o, params object[] pattern) => o;
public static T To<T>(this T o, out T x) => x = o;
如果使用structs[value types],类似的扩展方法也会很有用
public static TR Let<T, TR>(this T o, TR y) => y;
尽情享受吧 我要做的是使用csharp ref关键字。例如:
ref MySubClassType e = ref MyMainClass.MySubClass;
然后可以使用快捷方式,如:
e.property
而不是MyMainClass.MySubClass.property
这里是的忠实粉丝
这就是我目前的C代码:
你可以用
With New HttpClient
.BaseAddress = New Uri("http://mysite")
.Timeout = New TimeSpan(123)
.PostAsync( ... )
End With
你有被拍打手腕的危险-我发帖的时候也是但是,似乎在处置等方面使用语句可以获得的所有好处,而不需要额外的繁琐
注意:这可能会偶尔出错,因此仅对非关键代码使用它。或者根本没有。请记住:您有一个选择…我认为“使用”的壁橱是静态使用的,但只适用于静态的方法或属性。
e、 g
更多信息:
为了让生活更轻松,您可以使用垂直选择快速编辑内容
对我来说,我试图自动生成代码,需要为多个不同的类重用一个简单的变量,如“x”,这样我就不必不断生成新的变量名。我发现,如果我将代码放在大括号部分{},我可以限制变量的范围并多次重用它
请参见示例:
public class Main
{
public void Execute()
{
// Execute new Foos and new Bars many times with same variable.
double a = 0;
double b = 0;
double c = 0;
double d = 0;
double e = 0;
double f = 0;
double length = 0;
double area = 0;
double size = 0;
{
Foo x = new Foo(5, 6).Execute();
a = x.A;
b = x.B;
c = x.C;
d = x.D;
e = x.E;
f = x.F;
}
{
Bar x = new Bar("red", "circle").Execute();
length = x.Length;
area = x.Area;
size = x.Size;
}
{
Foo x = new Foo(3, 10).Execute();
a = x.A;
b = x.B;
c = x.C;
d = x.D;
e = x.E;
f = x.F;
}
{
Bar x = new Bar("blue", "square").Execute();
length = x.Length;
area = x.Area;
size = x.Size;
}
}
}
public class Foo
{
public int X { get; set; }
public int Y { get; set; }
public double A { get; private set; }
public double B { get; private set; }
public double C { get; private set; }
public double D { get; private set; }
public double E { get; private set; }
public double F { get; private set; }
public Foo(int x, int y)
{
X = x;
Y = y;
}
public Foo Execute()
{
A = X * Y;
B = X + Y;
C = X / (X + Y + 1);
D = Y / (X + Y + 1);
E = (X + Y) / (X + Y + 1);
F = (Y - X) / (X + Y + 1);
return this;
}
}
public class Bar
{
public string Color { get; set; }
public string Shape { get; set; }
public double Size { get; private set; }
public double Area { get; private set; }
public double Length { get; private set; }
public Bar(string color, string shape)
{
Color = color;
Shape = shape;
}
public Bar Execute()
{
Length = Color.Length + Shape.Length;
Area = Color.Length * Shape.Length;
Size = Area * Length;
return this;
}
}
在VB中,我会使用With,而根本不需要变量“x”。不包括Foo和Bar的vb类定义,vb代码为:
Public Class Main
Public Sub Execute()
Dim a As Double = 0
Dim b As Double = 0
Dim c As Double = 0
Dim d As Double = 0
Dim e As Double = 0
Dim f As Double = 0
Dim length As Double = 0
Dim area As Double = 0
Dim size As Double = 0
With New Foo(5, 6).Execute()
a = .A
b = .B
c = .C
d = .D
e = .E
f = .F
End With
With New Bar("red", "circle").Execute()
length = .Length
area = .Area
size = .Size
End With
With New Foo(3, 10).Execute()
a = .A
b = .B
c = .C
d = .D
e = .E
f = .F
End With
With New Bar("blue", "square").Execute()
length = .Length
area = .Area
size = .Size
End With
End Sub
End Class
C#version 9中引入了带有
键的!
您可以使用它创建对象的副本,如下所示
personbrother=拥有{FirstName=“Paul”}的人;
上行创建了一个新的Person记录,其中LastName属性是Person的副本,FirstName是“Paul”。您可以在with表达式中设置任意数量的属性。除“克隆”之外的任何合成成员“方法可能由您编写。如果记录类型具有与任何合成方法的签名匹配的方法,则编译器不会合成该方法。”
更新:
在撰写此答案时,C#9尚未正式发布,只是在预览中发布。不过,它将于2020年11月与.NET 5.0一起发布
有关更多信息,请查看。我知道这上面有一个副本,但就我的一生而言,我无法找到一个可以找到它的搜索查询。@ctacke:我想“不会那么难…”,然后花了10分钟试图找到它,但没有成功。…谷歌知道:“使用c#站点:stackoverflow.comgives:不,using语句是非常不同的-using语句的要点是在块的末尾处理资源。这并没有使引用值的时间缩短。谢谢Jon,学习另一门语言总是很好,我想我应该注意“假设使你和我变成一个傻瓜”这句老话,但我猜在这种情况下,只有我看起来很糟糕;)不。。。初始值设定项仅在初始化时起作用。。。看看流畅的界面吧!没有理由使用无法缩短引用值的时间(借用上面的答案):使用(var c=cell.Border(xlEdgeT
struct Point
{
public double X;
public double Y;
public string Name;
}
static Point Sample0() => new Point().To(out var p).With(
p.X = 123,
p.Y = 321,
p.Name = "abc"
).Let(p);
ref MySubClassType e = ref MyMainClass.MySubClass;
if (SKYLib.AccountsPayable.Client.ApiAuthorization.Authorization.AccessTokenExpiry == null || SKYLib.AccountsPayable.Client.ApiAuthorization.Authorization.AccessTokenExpiry < DateTime.Now)
{
SKYLib.AccountsPayable.Client.ApiAuthorization.Authorization.Refresh();
_api = new SKYLib.AccountsPayable.Api.DefaultApi(new SKYLib.AccountsPayable.Client.Configuration { DefaultHeader = SKYLib.AccountsPayable.Client.ApiAuthorization.Authorization.ApiHeader });
}
With SKYLib.AccountsPayable.Client.ApiAuthorization.Authorization
If .AccessTokenExpiry Is Nothing OrElse .AccessTokenExpiry < Now Then .Refresh()
_api = New SKYLib.AccountsPayable.Api.DefaultApi(New SKYLib.AccountsPayable.Client.Configuration With {DefaultHeader = .ApiHeaders}
End With
Using oClient As HttpClient = New HttpClient
With oClient
.BaseAddress = New Uri("http://mysite")
.Timeout = New TimeSpan(123)
.PostAsync( ... )
End With
End Using
With New HttpClient
.BaseAddress = New Uri("http://mysite")
.Timeout = New TimeSpan(123)
.PostAsync( ... )
End With
using static System.Math;
...
public double Area
{
get { return PI * Pow(Radius, 2); } // PI == System.Math.PI
}
public class Main
{
public void Execute()
{
// Execute new Foos and new Bars many times with same variable.
double a = 0;
double b = 0;
double c = 0;
double d = 0;
double e = 0;
double f = 0;
double length = 0;
double area = 0;
double size = 0;
{
Foo x = new Foo(5, 6).Execute();
a = x.A;
b = x.B;
c = x.C;
d = x.D;
e = x.E;
f = x.F;
}
{
Bar x = new Bar("red", "circle").Execute();
length = x.Length;
area = x.Area;
size = x.Size;
}
{
Foo x = new Foo(3, 10).Execute();
a = x.A;
b = x.B;
c = x.C;
d = x.D;
e = x.E;
f = x.F;
}
{
Bar x = new Bar("blue", "square").Execute();
length = x.Length;
area = x.Area;
size = x.Size;
}
}
}
public class Foo
{
public int X { get; set; }
public int Y { get; set; }
public double A { get; private set; }
public double B { get; private set; }
public double C { get; private set; }
public double D { get; private set; }
public double E { get; private set; }
public double F { get; private set; }
public Foo(int x, int y)
{
X = x;
Y = y;
}
public Foo Execute()
{
A = X * Y;
B = X + Y;
C = X / (X + Y + 1);
D = Y / (X + Y + 1);
E = (X + Y) / (X + Y + 1);
F = (Y - X) / (X + Y + 1);
return this;
}
}
public class Bar
{
public string Color { get; set; }
public string Shape { get; set; }
public double Size { get; private set; }
public double Area { get; private set; }
public double Length { get; private set; }
public Bar(string color, string shape)
{
Color = color;
Shape = shape;
}
public Bar Execute()
{
Length = Color.Length + Shape.Length;
Area = Color.Length * Shape.Length;
Size = Area * Length;
return this;
}
}
Public Class Main
Public Sub Execute()
Dim a As Double = 0
Dim b As Double = 0
Dim c As Double = 0
Dim d As Double = 0
Dim e As Double = 0
Dim f As Double = 0
Dim length As Double = 0
Dim area As Double = 0
Dim size As Double = 0
With New Foo(5, 6).Execute()
a = .A
b = .B
c = .C
d = .D
e = .E
f = .F
End With
With New Bar("red", "circle").Execute()
length = .Length
area = .Area
size = .Size
End With
With New Foo(3, 10).Execute()
a = .A
b = .B
c = .C
d = .D
e = .E
f = .F
End With
With New Bar("blue", "square").Execute()
length = .Length
area = .Area
size = .Size
End With
End Sub
End Class