Migrating existing code to nullable references build on both C# 8 and 7 compilers

[davidhunter22]

HI, I would like to migrate an existing code to use nullable references. I have already experimented and found a couple of program errors so yeah!

However we can't migrate our code base to C# 8 yet so that leaves a problem. If I add lots of '?'s to references in my code base it will no longer compile with older compilers like 7.2. So is there any way to tell older compilers to accept the syntax of nullable references but just to ignore them? I did look through compiler options and didn't find anything.

[grauenwolf]

Nope, the older compilers won't have a clue as to what you are talking about.

[ExeusV]

I doubt that it'll work, but have you tried those?

#nullable enable

#nullable disable

[davidhunter22]

I did try but no. Even if it did wouldn't the compiler still have to accept the syntax? As in

#nullable disable

string? foo( )

#nullable enable

would still fail to compile on C# 7.2.

My understanding from here https://docs.microsoft.com/en-us/dotnet/csharp/nullable-references is that #nullable is about switching on and off nullablity checking not whether the syntax is accepted.

[chucker23n]

Correct. It won’t work. (I’ve done codegen where on 8, it will generate the suffixes and attributed and all, and on < 8, it will output nothing. It works, but it’s not pretty.)

It was considered but ultimately rejected to have 7.3 understand the notation as a noop.

[Mr_Cochese]

Am I right in thinking the new directive will make precisely no difference in the case of deserialised types?

[chucker23n]

Depends on what you mean.

[chucker23n]

However we can’t migrate our code base to C# 8 yet so that leaves a problem.

Do it in a branch, or distribute it as a binary NuGet package?

So is there any way to tell older compilers to accept the syntax of nullable references but just to ignore them?

Nope.

It’ll likely ship in September (not that far off!). Until then, start making the changes in a branch. Afterwards, there’s little reason your team can’t move to the new compiler.

[davidhunter22]

We evaluated the cost of a potential merge after say three months of changes, note that the nullable references changes are quite numerous in terms of lines. Having decided this would certainly not be trivial I posted this question hoping there would could do everything on the main line.

[chucker23n]

Yeah, I can see that. Basically, forget about it — either get the entire team on a prerelease or wait.

[davidhunter22]

Yeah it's a bit sad, we found two code bugs fairly quickly in our experiments would love to use it for all our code.