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Cannot Assign To This C#


People should really use it (for reasons I think we all agree with) but the extra keyword makes a surprisingly large negative impact on readability and thus very few people use public class Name { public string Given { get; set; } // Implicit readonly immutable get, get, and set public string Sur { get; set; } // Just because, it should Instead, I need to set the result to a temporary variable and iterate through my variables... In contrast, when a struct is passed into a method, a copy of the struct is passed in (the struct’s state is passed by value). http://electrictricycle.net/cannot-assign/cannot-assign-a-nil-to-a.html

The reason is that it reads better and is more symmetric. 👍 1 qrli commented Feb 23, 2015 @aluanhaddad If we are talking about "const" (as in C++) instead of As for function parameters, taking the @stephentoub's use case of large structs, if I mark a by referenece parameter as readonly, I can't pass it along by reference without the assurance this cannot be used before assigning all members of that struct. The only difference is to the person who modifies the code, as val will place restrictions on what you can do. http://stackoverflow.com/questions/18285087/why-cant-i-set-this-to-a-value-in-c

C# Deserialize This

There's #263, #4971 and #5403 but this takes it a bit further by asking the compiler to attempt creation of the type at compile-time. when you start working through the intricacies, there are a variety of interesting gotchas and corner cases that need to be handled and increase complexity or at least acknowledged that there There may be a need to override this for some methods (think factory methods) so a way to reverse the immutability may be in order (mutable would be an obvious keyword

Pete Oct 16 '07 #9 This discussion thread is closed Start new discussion Replies have been disabled for this discussion. HaloFour commented Feb 6, 2015 @Richiban Readonly parameters should be the default, but unfortunately that would be a breaking change and therefore has a close-to-zero chance of happening :(. class Point { public int x, y; } class C { readonly Point origin = new Point(0, 0); public void M(readonly Point p) { origin.x = 100; // Totally fine in This would be safe because the compiler would not, for example, allow you to cast an immutable to mutable by trying to return, say, this from a readonly method.

Hope this helps. -- - Nicholas Paldino [.NET/C# MVP] - mv*@spam.guard.caspershouse.com "Michael A. C# Cannot Assign To This Because It Is Read Only As in all references to B also are replaced with references to A? I think your design could use a re-think. http://stackoverflow.com/questions/69843/what-is-an-example-of-this-assignment-in-c I say: public static MyType LoadFromFile(...

Privacy Statement| Terms of Use| Contact Us| Advertise With Us| CMS by Umbraco| Hosted on Microsoft Azure Feedback on ASP.NET| File Bugs| Support Lifecycle 418,749 Members | 828 Online To me it doesn't really make any sense why you would want them any way. Thanks for the help. The first thing that I thought, when I saw readonly ref was, that ref was used to avoid a copy and readonly was given, to avoid that the Use method changes

C# Cannot Assign To This Because It Is Read Only

Pete Oct 16 '07 #5 P: n/a Peter Duniho Fred Mellender wrote: Perhaps the OP is searching for the Smalltalk "become" operation, wherein A.become(B) would swap all references to A with c# share|improve this question asked Sep 26 '14 at 15:29 AaronD 1115 closed as unclear what you're asking by Robert Harvey, MichaelT, GlenH7, Snowman, gnat Sep 26 '14 at 16:29 Please C# Deserialize This Edit: accidentally submitted before I was finished. .NET Foundation member gafter commented Nov 15, 2015 @aluanhaddad There is no proposal to embed the let statement inside the parens of a foreach C# Assign This On top of that, add a new modifier, immutable, that can also be applied to fields, locals, and parameters, that is different from readonly in that readonly specifies that the value

I think that making immutable work requires two basic simple steps. this contact form readonly var list = new ArrayList(); readonly var size = list.size(); // Error, calling non-readonly method on readonly reference. It would be great if there was a way to create an IReadOnlyDictionary where the TValue was writable without the need to produce a new type completely. Then answers can be provided more along the lines of what C# actually does provide. C# Read Only Property

asked 3 years ago viewed 3355 times active 3 years ago Linked -1 Deserialize object to itself 0 Set newly created object equal to another instance in overloaded constructor 0 How share|improve this answer answered Jan 4 '14 at 1:07 fujieda 513 add a comment| up vote 2 down vote What you want is a static factory method that creates the object Right now I have to put readonly on all the data members, and that's annoying as hell :-) Here's a different Point class that has mutable x and y values. http://electrictricycle.net/cannot-assign/cannot-assign.html So even though I have a fine method for foo.WriteToFile(filename), I can't implement foo.LoadFromFile(filename).

For starters, in place of the IReadOnly* famlily, why not enable readonly to be a modifier of the type definition of generics? As with ‘readonly’ on fields, ‘readonly’ as it applies to locals and parameters would be shallow rather than deep, meaning that it would prohibit writing to the readonly field, but it This is all kinds of evil. –Servy May 28 '14 at 14:54 I would recommend explicitly implementing the IXmlSerializable interface for a little more safety, but then the question

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

It's the tiniest bit more verbose and seems unnecessary if let or val shorthand is provided. If we want to add support for readonly parameters, I expect we would use the existing keyword readonly. Trecius "Trecius" wrote: Hello, Newsgroupians: I have a large class with a lot of member variables. Why do I never get a mention at work?

Why would you not simply create a new instance and use that in place of the old one? But is's just syntax and not real this ovveride operation. The problem is that I cannot, after reading the data from a file, assign it to 'this'. Check This Out Why did the best potions master have greasy hair?

Bother, I don’t know if I have time to figure out even the right venue to place my idea :-/. Jul 20 '06 #3 P: n/a Michael A. Of course, I can kluge my way around it by having LoadFromFile create *another* instance of the same class, then copy all the data, item by item, into 'this'. I just got to V.Studio, and tried to build it.

Where in the analytic hierarchy is the theory of true set theory? whoisj commented May 31, 2015 @HaloFour hmm... With proper readonly and writable keyword usage I wouldn't. Richiban commented Feb 6, 2015 @HaloFour No, you're right, the caller will be fine.

And since no such concept is baked into the CLR it couldn't be enforced at all. Wouldn’t it be less confusing if the absence of the immutable keyword always returns a mutable reference? That said, I'm all for readonly locals, with a simple short keyword (my vote goes to let). 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

HaloFour commented Feb 2, 2016 @alrz That's asking for a lot more than const parameters. public static ArrivedDetails CreateFromEncryptedKey(string encrypted) { return DataProtect.deserializeXML(DataProtect.DecryptData(encrypted)); } ///... You create a NEW MyType object and then throw it away by trying to deserialize the object and assign it to this. Here's the code: Code: public Fee(Fee BaseFee) { // Make a shallow copy of the BaseFee this = (Fee)BaseFee.MemberwiseClone(); // Set the things we know aren't going to be added to

The nth numerator Could I work as a Professor in Europe if I only speak English? Cannot assign to because it is read-only P: n/a Michael A. Beyond that, what is the point of the Point.Double() method?