Example seems incorrect.

[qsdfplkj]

This example makes no sense to me without the in keyword it is also still 44. The in keyword seems only usefull to state that the argument cannot be changed within the scope of the method.

        int readonlyArgument = 44;
        InArgExample(readonlyArgument);
        Console.WriteLine(readonlyArgument);     // value is still 44

    private static void InArgExample(in int number)
    {
        // Uncomment the following line to see error CS8331
       // number = 19;
    }

[Enter feedback here]

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Document Details

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• ID: 6b1434b0-5459-7569-47f7-46bf33fc3953
• Version Independent ID: 8a4ae81b-1ae5-cbe6-d58b-df455414e245
• Content: in parameter modifier - C# Reference
• Content Source: docs/csharp/language-reference/keywords/in-parameter-modifier.md
• Product: dotnet-csharp
• Technology: csharp-language-reference
• GitHub Login: @BillWagner
• Microsoft Alias: wiwagn

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Associated WorkItem - 448841

[svick]

If you don't specify any modifiers, parameters are passed by value. This means that the method has its own copy of the parameter and so modifying it does not affect the caller. Contrast this with the ref modifier, which is similar to in, except it allows modifications (and also requires adding ref to the caller).

This does mean that the in modifier is not useful very often, usually when the parameter is a large struct and you want avoid the overhead of copying it.

[qsdfplkj]

An example should show when/how it's useful. With or without in the value remains 44 after the method ends. If it doesn't make a copy for value types then show that in the example. It seems to save some memory but that is not clear from the example. Besides what about reference: should I use SomeMethod(in IEnumerable<int> numbers) or SomeMethod(IReadOnlyList<int> numbers)

[BillWagner]

I'll keep this open in our backlog. I think the best remedy is to add links from each of the language reference to a conceptual article that contrasts the behavior with:

• no modifier on the parameter
• in modifier
• ref modifier
• out modifier.