Results of running 'make member readonly' on IDE

[CyrusNajmabadi]

No description provided.

[sharwell]

❔ What's the point of this, considering there is no way to directly invoke this member such that it will benefit from the readonly designation?

[CyrusNajmabadi]

marks intent that it should not mutate state. can go along with anohter analyzer (or the compiler) that tells you if you violate this and actually mutate this guy (or cause it to be copied).

[sharwell]

I'm concerned this may add noise and/or confusion for people that don't understand how interface dispatch works today. In almost all cases where an explicitly interface implementation is called, the member is already operating on a copy that was created for that one call. Exceptions to this include:

1. The user is operating on a storage location which is statically-typed to the interface and not to the value type. In this case, the use of readonly isn't apparent to the caller at all.
2. The user has gone to strange lengths to ensure a constrained call is made without copying/boxing a value.

I see arguments for both keeping this behavior and skipping this behavior. Maybe discuss with the team before we merge?

[CyrusNajmabadi]

In almost all cases where an explicitly interface implementation is called, the member is already operating on a copy that was created for that one call. Exceptions to this include:

I actually disagree with this. :) Passing a value type to a generic that is constrained on an interface is a normal pattern, and we expect to push it further in C#.

The purpose of readonly here is important as a documentation/protection mechanism (similar to 'static' on a lambda). The presence of it means no chance of mutation happening in the future (similar to how 'static' prevents capture in the future).

I can bring to team to see. But this seems like a pure benefit. I'm not sure what could be bad/undesirable about marking these members this way :)

[sharwell]

❔ Why is this one not marked readonly, but the one below (SegmentedDictionary`2.cs) is?

[CyrusNajmabadi]

so the system is not multi-pass. so first pass mae T Current readonly. Another pass would then let followup members become readonly. This is similar to how 'make static' and otehr similar features work.

[sharwell]

❔ Is there any difference between { get; set; } and { readonly get; set; }?

[CyrusNajmabadi]

yes. it will allow hte compiler/analyzers to actually validate that the getter does not mutate/copy this.

[sharwell]

Note that I'm asking about literally this exact form, where in all cases the contents of both accessors are compiler-generated.

[CyrusNajmabadi]

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/struct#readonly-instance-members

[sharwell]

❔ Why mark the members readonly instead of the containing type?

[CyrusNajmabadi]

yeah, you get both messages here. and making the type readonly def makes sense.

[CyrusNajmabadi]

@sharwell have rerun using the updated logic you suggested.

[CyrusNajmabadi]

@sharwell ptal.