Personally I still think ReadOnlyCollection is the way to go, but if you REALLY want an array….. UpdateOther answers have suggested just casting collections to the newer IReadOnlyList, which extends IReadOnlyCollection to add an indexer. Unfortunately, this doesn’t actually give you betnova control over the mutability of the collection since it could be cast back to the original collection type and mutated. This prevents a client from accidentally making a variable with the same name.
About defensive copies
If you use a const in dll A and dll B references that const, the value of that const will be compiled into dll B. If you redeploy dll A with a new value for that const, dll B will still be using the original value. I would use a wrapper class that keeps everything read-only. This is for scalability, reliability and general readability. I have a class with various public properties which I allow users to edit through a property grid.
- Needless to say, this would cause consternation for other clients of the Color class.
- I believe this will get you the benefits of using a static variable within the module, the optimization opportunities of inlining, and the familiar interface of a getter function.
- So while the copy in ExtMethod3 could be removed, there will be no guarantees, and you would need to inspect the assembler to figure out if it is actually done.
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- Keep in mind that readonly only applies to the value itself, so if you’re using a reference type readonly only protects the reference from being change.
- The third option is the strongest, as far as enforcement goes, but it can result in duplication of code and is more of a refactoring effort.
Making C module variables accessible as read-only
The difference is that the value of a static readonly field is set at run time, so it can have a different value for different executions of the program. However, the value of a const field is set to a compile time constant. The only real reason for that preference is the general preference that .NET classes not have public fields. However, if that field is readonly, I can’t see how there would be any real objections other than a lack of consistency with other properties. The readonly keyword is used to declare a member variable a constant, but allows the value to be calculated at runtime.
If these are exposed a client as an object (you might do this for COM interop as I did) the client can manipulate array values. Use the Clone() method when returning an array as an object. I don’t believe there are any performance gains from using a readonly field.
Readonly instance fields
The second option is convenient, since implementing an interface is possible without much refactoring effort. Unfortunately, callers can still cast to the underlying type and attempt to write against it. Often, this option is combined with a read-only flag to ensure the immutability is not violated. Sometimes I want to user to be able to save (serialize) changes they’ve made to an instance of the class.
How to make a variable (not class member) “read only” in C#
- The key difference is that Const is the C equivalent of #DEFINE.
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- You can not get compile-time checks (like given with the keyword readonly) by changing a property to readonly at runtime.
- If your function is very long, it should be refactored into smaller functions.
- Eric Lippert of the C# team has more information on different types of immutability.
- TLDR; readonly on a struct method means that this is passed as a readonly reference to the method, rather than a normal reference like with non-readonly struct methods.
It’s just for doing exactly as you suggest, for preventing modification once it has been initialised. You can use PostSharp to create OnFieldAccessAspect that will not pass new value to any field when _readOnly will be set to true. With aspect code repetition is gone and there will be no field forgotten. But propably it is better to re-design access to the class. For example create a “writer class”, which checks if the underling “data class” can currently be written or not. The third option is the strongest, as far as enforcement goes, but it can result in duplication of code and is more of a refactoring effort.
For instance, there is no danger of passing an immutable structure to another random portion of code. They can’t changed it ever so you can program reliably against that structure. Don’t forget there is a workaround to get the readonly fields set outside of any constructors using out params. Now, can the code that is generated rely on the fact that A.C is a compile-time constant? I.e., can the use of A.C simply be replaced by the value 0? If you say “yes” to this, then that means that the developer of A cannot change the way that A.C is initialized — this ties the hands of the developer of A without permission.
I like that, besides the fact that the client needs to read the content of a pointer. Also, every read-only variable needs its extern const pointer to const. In practice, this means that a C or C++ program that wants to be portable has to avoid modifying constant strings. So yes, readonly methods pass this by reference, but so do other methods. Please see my answer below, it turns out the premise of my question is wrong, method calls on structs are already by reference.
How can I make a read only version of a class?
This differs from a constant declared with the const modifier, which must have its value set at compile time. Using readonly you can set the value of the field either in the declaration, or in the constructor of the object that the field is a member of. If you are creating a library, it is possible to define a public interface with a private/internal class. Any method which needs to return an instance of your read-only class to an external consumer should instead return an instance of the read-only interface instead.