csharplang/meetings/2022/LDM-2022-08-10.md

C# Language Design Meeting for August 10th, 2022

Agenda

1. required property default nullability

Quote of the Day

• "If I'm going on a long journey I always think I can get all this stuff done on the plane. I always end up watching a movie."

Discussion

required property default nullability

https://github.com/dotnet/csharplang/issues/6359

Today we looked at what the default state of required properties should be at the beginning of a constructor. As implemented and specified currently, properties will be treated as if they have the null state they claim, so public required string Prop { get; set; } would have a not-null state at the start of a constructor. We don't think this is a good idea: in C# 10, users could either count on a chained constructor having set all members, or will have the default state of all members set to not-null. We think required serves as a good heuristic indicator that the property should be set to default(T) at the start of the constructor. The exception to this is when the user chains to a constructor has specified SetsRequiredMembers on the constructor.

Conclusion

We accept the following rules:

1. When chaining to a constructor that does not have SetsRequiredMembersAttribute, all required members have a null state of default(T), including those required members from a base type.
2. At the end of a constructor that is attributed with SetsRequiredMembersAttribute, all required members must have the null state they are declared with, including those required members from a base type.