LDM Notes for April 7th, 2025

[333fred]

https://github.com/dotnet/csharplang/blob/main/meetings/2025/LDM-2025-04-07.md

Agenda

• Breaking change discussion: making partial members in interfaces virtual
• Interpolated string handler argument values

[hez2010]

we were the ones to discover it, rather than a bug being reported, and the behavior in methods has been around for a long time.

Doesn't this mean fixing the behavior for methods as well would only have a minor impact because it has been too rare to be even noticed? I would like to take the behavior change for methods as well when we can still fix it in a time that is not too late, instead of keeping the inconsistency.

[MauNguyenVan]

Inconsistency will make the language increasingly complex, especially when a developer refactors code from a method to a property—it can introduce potential bugs that are very hard to detect. Or, if in a team some people use it as a method while others use it as a property, it can lead to incorrect logic execution without the developers even realizing it.

With this fix, I don't think the issue is actually resolved. Instead, it still introduces potential hidden bugs.

[CyrusNajmabadi]

@MauNguyenVan we considered that, but accepted the tradeoff here.

[MauNguyenVan]

I'm checking in github public repo to check how many code base use this issue (partial interface with the default partial method and have other class/ interface overwrite the default partial method).

[jjonescz]

I've used this query to find partial methods in interfaces and it only returned static ones, no instance ones.

[MauNguyenVan]

Same me, but i will digging by download file matched content and check by regex later

[MauNguyenVan]

We will take this bugfix for partial properties and events, but not for methods. Since partial properties are so new, we will not tie it to language version unless divisional breaking change procedures require us to do so.

IMO, we should fix for both the method behavior and other members, it keeps language behavior is consistency for multiple types(property, indexer, method, event ...). We should add the breaking change for docs,

I guess, very less code base used/got it (this issue) because this is high-level feature, if has, they realized and maybe report a bug or ask it in StackOverflow, or at least they don't use it any more (it can be realize the expect behavior when read the code base, but the actual result is not).

You see, c# was designed so good, and after 20+ years, the language stills keeps the good design, I don't want C# to become C++ like, to much rules and tricks, inconsistency.