I see in the MSDN documentation of init keyword, it has code example as below, from the url: , from what I understand, the "YearOfBirth" in the beginning of the assignment "field = (YearOfBirth <= DateTime.Now.Year)" should be "value" keyword. Am I right? Or that is a new feature of a new C# version ? Thanks for your attention.

class Person_InitExampleFieldProperty
{
    public int YearOfBirth
    {
        get;
        init
        {
            field = (YearOfBirth <= DateTime.Now.Year)
                ? value
                : throw new ArgumentOutOfRangeException(nameof(value), "Year of birth can't be in the future");
        }
    }
}

I see in the MSDN documentation of init keyword, it has code example as below, from the url: https://learn.microsoft/en-us/dotnet/csharp/language-reference/keywords/init, from what I understand, the "YearOfBirth" in the beginning of the assignment "field = (YearOfBirth <= DateTime.Now.Year)" should be "value" keyword. Am I right? Or that is a new feature of a new C# version ? Thanks for your attention.

class Person_InitExampleFieldProperty
{
    public int YearOfBirth
    {
        get;
        init
        {
            field = (YearOfBirth <= DateTime.Now.Year)
                ? value
                : throw new ArgumentOutOfRangeException(nameof(value), "Year of birth can't be in the future");
        }
    }
}

• c#

• 2 You're right, it should be value, as is, the test's result is always true since YearOfBirth is 0 when the test is executed – vc 74 Commented Nov 20, 2024 at 19:46
• 4 As noted right after the code sample, The field keyword is a preview feature in C# 13. So, the code is correct and works as expected, but only in C#13 with preview features enabled. – Serg Commented Nov 20, 2024 at 20:13
• 1 @Serg I don't think it does, the test should clearly check the new YearOfBirth value, not the old one – vc 74 Commented Nov 21, 2024 at 17:33
• @vc74, yes, you are right. From a validation logic point of view it should be value there. – Serg Commented Nov 21, 2024 at 18:38
• @Serg: field keyword? It could be something different: a private field with this name, (omitted by IcyBrk). Nothing prevents using this name. I followed the naming of the question and used this name in my answer. Of course, it works. – Sergey A Kryukov Commented Nov 24, 2024 at 0:49

1 Answer 1

Yes, what you show does work, with value, but you also may find the alternative syntax more convenient and clear. Consider this very simplified example:

class InitOnlyDemo {
    internal InitOnlyDemo() { CaseB = 42; }
    int field = 0;
    internal int CaseA {
        get { return field; }
        init { field = value; } }
    internal int CaseB { get; init; }
    public int CaseC { get; private protected set; }
}

Your case is the property CaseA. With CaseB, you rely on automatically implemented getter and then init simply indicates “initialization-only” and leaves the initialization itself to the constructor. Finally, CaseC uses automatically implemented getter and setter and also demonstrates a way to prescribe different access modifiers for getters and setters.