Field nullability

[NN---]

How can I specify that field must have non null value when assigned but until that it doesn't hold any value ?
It would be nice to have some attribute for this behavior:

#nullable enable

class A
{
  [MemberNotNull] // Proposal: null value cannot be assigned
  string? something; // null now

 
  public string F(string x) => something ??= x; // OK

  public string G(string? y) => something ??= y; // Error, null value cannot be assigned.
}

[Joe4evr]

[DisallowNull]
string? something;

[canton7]

See this on SharpLab.

See this article for a good run-down on (most of) the NRT-related attributes.

[NN---]

@Joe4evr Thanks.
It is discovered that ReSharper showed me error for such code.
But in fact there is no compilation issue.
Opened an issue for ReSharper.

[NN---]

@Joe4evr It turns out that this works unexpectedly :)
dotnet/roslyn#49903
dotnet/roslyn#49911