c#-7.0

问题 Can I await on a Task that was created on a different thread? For example: ... CurrentIteration = Execute(); // returns Task await CurrentIteration; ... And then, on another thread: ... await CurrentIteration; ... Will the second thread wait for method Execute to finish executing? If it will, will I be able to re-use CurrentIteration for the same purpose in the second thread, given that I re-run CurrentIteration = Execute(); // returns Task await CurrentIteration; On the first thread? I tried

问题 I am not sure how to use new C# 7 features in existing solution. I tried using pattern matching in a switch statement but I keep getting Value of integral type expected error. Is there a trick to enable it? I though I can just use new features if I open the solution in VS 2017. My projects are targeting .net 4.6.2. Here is the sample code private void CS7Test(object o) { switch (o) { case null: Console.WriteLine("it's a constant pattern"); break; case int i: Console.WriteLine("it's an int");

问题 If I set the LangVersion to 7, I get the following error: Error:CS1617: Invalid option '7' for /langversion; must be ISO-1, ISO-2, Default or an integer in range 1 to 6. I can't install Visual Studio 2017. 回答1: Unfortunately for now it is not possible on mac/linux, but it is planned - around Q1 2017. Source: https://rider-support.jetbrains.com/hc/en-us/community/posts/205987804-Rider-and-C-7- 来源： https://stackoverflow.com/questions/42830694/enabling-c-sharp-7-compilation-in-project-rider

问题 I was playing arround with the Value Tuple in C#. First some demo data: #region Data public class Product { public string Name { get; set; } public int CategoryID { get; set; } } public class Category { public string Name { get; set; } public int ID { get; set; } } public class Data { public List<Category> Categories { get; } = new List<Category>() { new Category(){Name="Beverages", ID=001}, new Category(){ Name="Condiments", ID=002}, }; public List<Product> Products { get; } = new List

问题 I was wondering if there is a way to do something like this in c# 7 var test = "aaeag"; switch (test) { case test.StartsWith("a"): break; default: break; } Sadly it does not look like it possible. Is this correct or am I doing something wrong? 回答1: This is possible with C# 7, using a when guard: var test = "aaeag"; switch (test) { case var s when s.StartsWith("a"): break; default: break; } What your version of the code is doing is often referred to as active patterns . By eg defining the the

问题 Is it possible to use the ref returns feature in C# 7.0 define a generic function that can do both comparison and update of a field in two instances of an Object? I am imagining something like this: void UpdateIfChanged<TClass, TField>(TClass c1, TClass c2, Func<TClass, TField> getter) { if (!getter(c1).Equals(getter(c2)) { getter(c1) = getter(c2); } } Example intended usage: Thing thing1 = new Thing(field1: 0, field2: "foo"); Thing thing2 = new Thing(field1: -5, field2: "foo");

问题 I'm trying ValueTuple Class in C#, and i have a doubt about properties naming, let's see: If instantiate a ValueTuple declaring the object like this: var tuple1 = (Name: "Name1", Age: 25); We can name the properties, but, like this: ValueTuple<string,int> tuple2 = (Name: "Name1", Age: 25); we get a warning that says the names are ignored,so We should type: ValueTuple<string,int> tuple2 = ("Name1",25); Then the properties will be tuple2.Item1 and tuple2.Item2 Can someone explain this newbie

问题 From Microsoft new-features-in-c-7-0: public void PrintStars(object o) { if (o is null) return; // constant pattern "null" if (!(o is int i)) return; // type pattern "int i" WriteLine(new string('*', i)); } Whats the diferrence of o == null and o is null ? 回答1: The o is null is translated to object.Equals(null, o) (you can see it here). The object.Equals code is written as: public static bool Equals(Object objA, Object objB) { if (objA == objB) { return true; } if (objA == null || objB ==

问题 C#7 introduces a new feature called patterns , which you can use with Is-Expression or Switch cases like this: string str = null; switch(str){ case string x: Console.WriteLine("string " + x); break; default: Console.WriteLine("default"); break; } and you would expect that it will goes inside case #1, as it is the same type, but it didn't. 回答1: Despite what you might think, string x = null actually isn't a string at all. It is 'nothing', assigned to a variable of type string. The check in your

问题 We have the following code that has been working fine in our UWP app until today after we updated Visual Studio 2017 to the latest 15.3 . private void Test() { var groups = new List<(Guid key, IList<(string, bool)> items)>(); var items = new List<(string, bool)> { ("a", true), ("b", false), ("c", false) }; var group = (Guid.NewGuid(), items); groups.Add(group); } There is no error message but this in the output window Tuple element name 'items' is inferred. Please use language version 7.1 or