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Cannot Assign To This Because It Is Read-only Constructor


I like let because it's already a keyword in C# that behaves in a nearly identical way and because it's not without precedent. Suppose I have two functions called DoubleSizes() and Double(). An unfortunate choice of example, IMHO. .NET already has a Point type, and it's a struct. You've reached the point where your domain objects are loading data themselves and you've realised you'll be writing repetitive mapping code. http://electrictricycle.net/cannot-assign/cannot-assign-to-this-because-it-is-read-only-c.html

This way, if an object only provides a readonly implementation (which is safe to call on both mutable and immutable references), it can be directly called. Instead, I need to set the result to a temporary variable and iterate through my variables... I'm thinking more of reasoning the contents of a method. The problem is that I cannot, after reading the data from a file, assign it to 'this'. my review here

C# Deserialize This

If I used a static method, the syntax would be this: MyType myobj = MyType.LoadFromFile(@"C:\blah\blither.xml"); which is more concise. Personal Open source Business Explore Sign up Sign in Pricing Blog Support Search GitHub This repository Watch 900 Star 6,483 Fork 1,552 dotnet/roslyn Code Issues 3,236 Pull requests 140 Projects Allow methods and getters/setters to be marked readonly as described by @jonathanmarston. You would be replacing the "this" reference altogether.

Are you confused about the difference between a struct and a class? See the How to Ask page for help clarifying this question.If this question can be reworded to fit the rules in the help center, please edit the question. 4 Actually, However, when the struct is large (for example, the System.Windows.Media.Media3D.Matrix3D struct contains 16 doubles, making it 128 bytes in size), it can become quite expensive to continually pass around copies of In my opinion if you consider let to be a binding to an expression rather than a variable declaration it doesn't really matter that it is a verb.

It wouldn’t // be allowed to write to any fields, which is what matters. It's replacing the instance reference altogether. EXA: Point temp = this.DoubleSizes(); this.x = temp.x; this.y = temp.y; return this; Yes, if you want the original instance to be the same instance after the operation, you will have http://programmers.stackexchange.com/questions/257309/in-c-can-i-do-this-outside-of-a-constructor And, of course, it should be possible to assign an object reference member of a readonly struct to a local variable but only to an immutable one.

stephentoub referenced this issue Jan 29, 2015 Open Proposal: Immutable Types #159 Pilchie added the Area-Language Design label Jan 29, 2015 lawrencejohnston commented Jan 29, 2015 And I think trying to So I vote for readonly locals, but against readonly parameters. [1] http://blogs.msdn.com/b/ericlippert/archive/2008/05/14/mutating-readonly-structs.aspx aluanhaddad commented Nov 15, 2015 @gafter using let to declare local variables reads well in the pattern context of mikedn commented Feb 6, 2015 I've seen a lot of poorly written code but I've yet to see parameters modified in the middle of a method. Apple Swift uses var and let in virtually the same manner as this proposal.

C# Assign This

So even though I have a fine method forfoo.WriteToFile(filename), I can't implement foo.LoadFromFile(filename).One idea is that perhaps instead of LoadFromFile, I need a constructorthat takes a filename as an argument. More Help I'm neither here nor there regarding readonly var. C# Deserialize This In addition, it would be helpful if you could try to clarify what it is exactly you're trying to do. C# Read Only Property You can use something like MemberwiseClone() to create an exact value-for-value duplicate of a class, if you're looking for getting two different instances (for example, you want to modify one without

Perhaps their code is wrong.For simplicity, suppose I have a Point class that two members: x and y.Suppose I have two functions called DoubleSizes() and Double().DoubleSizes() is defined as...public Point DoubleSizes(){ his comment is here If you choose to participate, the online survey will be presented to you when you leave the Msdn Web site.Would you like to participate? Can I get a dual entry Schengen visa for tourism purpose for me and my wife? Instead, I need to set the result to a temporary variable and iterate through my variables...

DoubleSizes() is defined as... http://www.dofactory.com/Patterns/PatternMemento.aspx HTH, Sam ------------------------------------------------------------ We're hiring! Pete Oct 16 '07 #4 P: n/a Fred Mellender Perhaps the OP is searching for the Smalltalk "become" operation, wherein A.become(B) would swap all references to A with a reference to this contact form this = null; will not work.

drewnoakes commented Jan 28, 2015 @ryancerium, I suppose this feature would require new metadata in the type system, therefore a new CLR and at the same time a new BCL. I don't know why you would want that, given that a foreach loop control variable is already readonly. static Person getByID(long ID){ return DataManager.Find(typeof(Person),ID); }   Then to use the function all you have to do is Person myPerson=Person.getByID(1234); Also it seems like you're using generics in your find

One idea is that perhaps instead of LoadFromFile, I need a constructor that takes a filename as an argument.

Is it just possible to reassign "this?" Again,I've seen some C# code changing the value of this, but are they in violationof a compile rule?Thank you, all. For example: public class FooManipulator { private Foo _myFoo; public void bar() { var allTheFoos = otherClass.FindAllFoos(); foreach(foo f in all) { if(f.id == 42) { this._myFoo = f; break; } Thanks ------------------------------------------------------------ This posting is provided "AS IS" with no warranties, and confers no rights. ‹ Previous Thread|Next Thread › This site is managed for Microsoft by Neudesic, LLC. | © I believe that programmers should be encouraged into programming with immutability in mind, and having a nice, short keyword will facilitate this :).

I think it better for const tobe shorthand for readonly ref. Other than that, it's a simple case of having to refactor the code. EXA: Point temp = this.DoubleSizes(); this.x = temp.x; this.y = temp.y; return this; Again, this is a small example. http://electrictricycle.net/cannot-assign/cannot-assign-to.html I can imagine also supporting readonly as a modifier for locals if we allow it for parameters, though I do not imagine it would be used much given the more concise

Vice-a-versa? public class Box { public T Value; } public struct Incrementor { private int value; public Incrementor(int initialValue) { this.value = initialValue; } public int Increment() { this.value += 1; return What direction should I be heading in, here? It would exclusively be for developers to ensure that they don't accidentally overwrite the existing value. … On Feb 6, 2015 10:39 AM, "Richard Gibson" ***@***.***> wrote: @MgSam Perhaps you're

What is exactly meant by a "data set"? Hot Network Questions What did John Templeton mean when he said that the four most dangerous words in investing are: ‘this time it’s different'? val foo = 123; var bar = 123; Compared to: let foo = 123; var bar = 123; I think the second version is much more 'scannable'. .NET Foundation member stephentoub Cannot assign to because it is read-only P: n/a Michael A.

A config = DataProtect.deserializeXML(DataProtect.DecryptData(encrypted)); foreach (var property in GetType().GetProperties()) if (property.GetCustomAttributes(typeof (XmlIgnoreAttribute), false).GetLength(0) == 0) property.SetValue(this, property.GetValue(tmp, null), null); This assigns the deserialized object to a temporal variable, and copy the You can assign to this for a struct, but then a struct can't be null because its a value type. In that case you want static method that performs creation of a class instance and returns instance of an object: public static Development CreateDevelopment(string developmentID) { return DevelopmentDS.GetDevelopment(developmentID); } The pattern