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C# Cannot Modify The Return Value Of Because It Is Not A Variable


Related 308What's the difference between struct and class in .NET?930When to use struct?2Is it possible to change the default value of a primitive data type?8Using Structs with WCF Services4Cannot assign property In contrast, classes arepassed by reference, that isa reference to the orginal instance is returned. Sry for this guys but there we some people explaining the difference and the why pretty precisely and others still complain why it is not in c# to modify structs. May 15 '07 #30 P: n/a Peter Duniho On Tue, 15 May 2007 15:07:56 -0700, Ben Voigt Check This Out

I'll try to be moreclear in the future. But for methods, the method could be doing anything, and the compiler doesn't really know what that is. because you must admit that doing it that way looks very straightforward :) Oh, absolutely it does. more hot questions question feed lang-cs about us tour help blog chat data legal privacy policy work here advertising info mobile contact us feedback Technology Life / Arts Culture / Recreation http://stackoverflow.com/questions/51526/changing-the-value-of-an-element-in-a-list-of-structs

C# Cannot Modify The Return Value Of Because It Is Not A Variable

I agree that this particular example is somewhat confusing. But you have to remember to work this way, not only when using the List but everywhere you want to change a field inside the struct. Structs have all kinds of gotchas, but if you follow that guideline the compiler will protect you from them.

Zytan May 16 '07 #37 P: n/a Peter Duniho On Wed, 16 May 2007 06:38:41 -0700, Ben Voigt >As applied to function declarations, I don't see how "const" enables anyof those optimizations.

I know it lacks this information. C# Modify List Item Why there are no approximation algorithms for SAT and other decision problems? A friendly warning: struct to class (or vice versa) is a big jump in C#. You will then get a reference to a Map object instead of an intermediate copy and you will be able to modify the object.

It's wildly different from C++ in many ways. C# Mutable Struct Modifying List items (generics) P: n/a Ivan Voras For a declaration like: Listlikewise the compiler can't make optimizations requiring constant values based on non-constant values.

C# Modify List Item

Fill in your details below or click an icon to log in: Email (required) (Address never made public) Name (required) Website You are commenting using your WordPress.com account. (LogOut/Change) You are https://social.msdn.microsoft.com/Forums/vstudio/en-US/6c925d84-2855-4a6d-a781-a269dd3b1eea/why-couldnot-i-modify-the-value-of-item-from-generic-collectionsnet-framework-20-?forum=csharpgeneral There's a time and place for a value type, and in fact they even have their place in lists. C# Cannot Modify The Return Value Of Because It Is Not A Variable example: List list = new List(); list.Add(new { Position = 1, Name = "abc" }); list.Add(new { Position = 2, Name = "def" }); list.Add(new { Position = 3, Name = C# List Change Value This helps a lot!

You can then modify the actual struct via an interface reference, which refers to the boxed object. his comment is here My gut feel is that what is shown is a smaller cut of a bigger picture in which there might even be better opportunities for functional decomposition of entity vs. How to import someone else's toolbox? And the compiler could check this while compiling the method. Update Value In List C# Using Linq

This will avoids effects like this. Or: void demo(int i) { int a[10]; for( int j = 0; j < 10000; j++ ) { a[13 * i % 7 + 3] += j; stuffit(i); } } With The problem (well, "a problem" anyway) is that lots of methods are essentially "const" even though no one's bothered to mark them as such. this contact form Yes, but you could mark them as "const" when the warning fires.

The compiler can't rely on the "const" keyword,because it can always wind up being cast away. C# Replace Element In List I will review value types and reference types. But it seems to me that other than some semantic oddities (that I've complained about myself :) ), the basic behavior is well-defined.

The same way C++ deals with const methods.

I claim that the main (conceptual) difference is that the former has _identity_, or can have identity, while the latter does not. If you create your own types (struct, class) you can just use public variables - no problem with that (but I hope you understand why this is considered bad practice...). There's nothing available to the compiler to let it know that the method changes the contents of the struct. (Remember when we warned you about making mutable structs, back in March? C# List Change Value At Index Subsets of C++ used by embedded compilers, perhaps (although in my experience they overload const and make it mandatory).

So, if I have a list of structs should I treat them as read-only? My feeling is that while it's possible theoretically to address the issue, I think it's simpler to just make the language simple and consistent, and require developers to understand that the One really wouldn't be able to know unless one examined myClass as well as the other code that put things in the list. navigate here How can I remove an Online Account?

it did for me :) If you really need structs to be stored in a collection and modified like you indicated in your question, you'll have to make your struct expose How can I declare independence from the United States and start my own micro nation? I wouldn't agree that the designers want you to use reference types when you can. When using a struct, it is better to make them immutable.

If you get a reference from a List<>, then yes you get a copy of the reference, just like you get a copy of a value type. That's why it's impossible to change references. For an example: const int nibbleCount = sizeof (int) * 2; char formatted[nibbleCount + 1] = { 0 }; char* ToHex(int n) { for( int i = 0; i < nibbleCount; On 14 May 2007 13:31:30 -0700, Bruce Wood wrote: >On May 14, 12:25 pm, Samuel R.

Been there, done that. It's worth clarifying here that the boxing itself is exactly the same as normal. Right. Good point.

Join & Write a Comment Already a member? Relying on the "const" keyword to enable a warning wouldn't have been a good idea in C++, because you'd get a lot of false positives due to the large amount of Can I use that to take out what he owes me? If you have a list of structs, the list is created on the stack, whereas a list of class objects will be created on the heap. >[quote]I need to find this

I've been changing all my ararys that are created dynamically (length unknown) into List<>, to avoid Array.Resize. On Tue, 15 May 2007 15:07:56 -0700, Ben Voigt [...]Understanding and using const-correctness is a prerequisite for being aprofessional C++ programmer. In the same way that overloading the "new" operator bugs me about reference types versus value types, you're dealing with a situation in which the indexing operator "[]" behaves differently depending