Is there a way you're supposed to work with the out keyword and nullable types?

[jklw10]

As you can see in this example, none of the ways that make sense to me work for getting the possible value out from the MathContext.Calculate()'s out argument.
the way i do it takes many more lines to make all the warnings go away.

I shouldn't have to use the ! operator right?

if i use ? it says cthird is now unassigned and spouts an error. which, it should be either null, or atleast allow you to accompany that out with a null.

here's how i see it should look.

[siegfriedpammer]

You should be able to use the NotNullWhenAttribute:

Example signature:

 public bool MatchLdLoc([NotNullWhen(true)] out ILVariable? variable)

Full example:

https://github.com/icsharpcode/ILSpy/blob/2ef3245158ca6d7001475115845af31855e578a8/ICSharpCode.Decompiler/IL/Instructions.cs#L8192-L8202

[jklw10]

Ah a good thing to learn for certain, but might not be possible if I wasn't the one writing the library. and the calculate() output isn't nullable the nullability is only in the MathPieces's components.

[yaakov-h]

You appear to be battling with definite assignment, not nullability.

Assuming that Token is a reference type, then you can simply call tokens[2].mathContext?.Calculate(out third2);. You don't need to use out var when you already have a variable that you want to assign the result to.

If Token is a value type, then you either need to match the nullability of third2 with the nullability of your out parameter, or you need that if block to wrap or unwrap the result.

[koszeggy]

Due to null short-circuiting this behavior is expected. If tokens[2].mathContext is null, then Calculate is not executed so your cthird remains unassigned. You even highlighted CS0165, which explains the issue.

But since you already initialized third2 there is no need to introduce another variable in the out parameter and then assign it to third2:

// This causes CS0165 because cthird will not be assigned if mathContext is null:
//Token third2 = Token.Invalid;
//tokens[2].mathContext?.Calculate(out Token cthird);
//third2 = cthird; // issue: cthird might be uninitialized here

// But you can simply do this:
Token third2 = Token.Invalid;
tokens[2].mathContext?.Calculate(out third2); // third2 is now assigned even if Calculate didn't execute

ps: and please avoid posting code as image because it's harder for us to answer if we cannot copy-paste it.

[jklw10]

static Token GetToken(MathPiece mp)
{
    if (mp.MathContext is not null)
    {
        mp.MathContext.Calculate(out Token cthird);
        return mp.Token ?? cthird;
    }
    return mp.Token ?? Token.INVALID;
}
static Token GetToken2(MathPiece mp)
{
    Token TokenOut = mp.Token ?? Token.INVALID;
    mp.MathContext?.Calculate(out TokenOut);
    return TokenOut;
}

the first one is what I Ended up with yesterday that works, but yeah the GetToken2()'s things could've been inside the the original piece of code without method extraction. which were written based on your suggestion.