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Proposal: read-only setter (again) #13048
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var personAlice = new Person() { Name = "Alice" }; How would this work? Object initializer is (mostly) just syntax sugar for calling the setter after the constructor returns. |
@svick You're right, my bad. Optional properties should better be initialized by an appropriate design pattern (e.g. builder) in this case. But for constructors it still stands. |
Such a thing cannot be a property setter. No method can update a I don't see much point to the idea. This validation belongs to the object creation, not to any property assignment. |
I think the general pattern you are alluding to could be
The compiler can statically verify that InitCount will only Such methods/property setters would only be allowed to be A potential problem would be
but the compiler could probably detect this case and error |
That is what I meant by streamlining the code into the constructor. In my eyes, the verification code does totally belong to the property itself instead of being written in the constructor. With one exception: complex interaction with other read-only fields. But that'll be rather rare, doesn't it? In most cases it will probably be something like a range validation or so, setting reasonable values or throwing exceptions when violated. BTW, when talking about evacuating the code in setters it should also be possible to attach @bradphelan I get your idea, but cannot currently think of any frequently used scenarios, except for properties in a builder like fashion. |
@lachbaer If you are talking about attaching readonly to methods then we are |
You are right, in a way. Properties are ad-hoc inline classes (state + behavior). What you really want is to introduce a proper one: class Name
{
public Name(string value)
{
Value = value ?? "(noname)";
}
public string Value { get; }
} Ideally this: class Name : string
{
public Name(string value) : base("(noname)")
{
}
} |
@dsaf Yes, that's a way to achieve it. But with significantly more code, also cluttering the namespace with otherwise useless classes or structs (for value types). Also there will be some more code around to make this work ( And also that gets me back to my proposal #8364. public readonly string Name
{
get;
readonly set { field = value ?? "(noname)"; } // internally set_Name(string value, ref string field)
} That's much leaner I think!
|
In practice you are likely to benefit from re-using in medium/large size projects.
Implicit conversion operator can be implemented if desired. |
Sure, but I'm talking about small projects or prototyping. |
I do what @dsaf suggested but with a struct rather than a class, sacrificing control of default(Name) for better memory and perf. I swear by custom types like this for all domain logic. It's paid off. |
We are now taking language feature discussion in other repositories:
Features that are under active design or development, or which are "championed" by someone on the language design team, have already been moved either as issues or as checked-in design documents. For example, the proposal in this repo "Proposal: Partial interface implementation a.k.a. Traits" (issue 16139 and a few other issues that request the same thing) are now tracked by the language team at issue 52 in https://github.com/dotnet/csharplang/issues, and there is a draft spec at https://github.com/dotnet/csharplang/blob/master/proposals/default-interface-methods.md and further discussion at issue 288 in https://github.com/dotnet/csharplang/issues. Prototyping of the compiler portion of language features is still tracked here; see, for example, https://github.com/dotnet/roslyn/tree/features/DefaultInterfaceImplementation and issue 17952. In order to facilitate that transition, we have started closing language design discussions from the roslyn repo with a note briefly explaining why. When we are aware of an existing discussion for the feature already in the new repo, we are adding a link to that. But we're not adding new issues to the new repos for existing discussions in this repo that the language design team does not currently envision taking on. Our intent is to eventually close the language design issues in the Roslyn repo and encourage discussion in one of the new repos instead. Our intent is not to shut down discussion on language design - you can still continue discussion on the closed issues if you want - but rather we would like to encourage people to move discussion to where we are more likely to be paying attention (the new repo), or to abandon discussions that are no longer of interest to you. If you happen to notice that one of the closed issues has a relevant issue in the new repo, and we have not added a link to the new issue, we would appreciate you providing a link from the old to the new discussion. That way people who are still interested in the discussion can start paying attention to the new issue. Also, we'd welcome any ideas you might have on how we could better manage the transition. Comments and discussion about closing and/or moving issues should be directed to #18002. Comments and discussion about this issue can take place here or on an issue in the relevant repo. I am not moving this particular issue because I don't have confidence that the LDM would likely consider doing this. |
[Other topics are already closed}
In my eyes a validation check for a read-only property value belongs to the property, thus the setter.
I suggest the
readonly
modifier for the setter:As the setter is
readonly
So the constraint check is in the place where it belongs and all requirements for read-onlys are met.
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