CallerArgumentExpression always null

Question

I'm experimenting with [CallerArgumentExpression] in C# 8:

static void Main(string[] args)
{
    try
    {
        Program query = null;
        Argument(query != null, "Ooops");
    }
    catch (Exception e)
    {
        Console.WriteLine(e.Message);
    }
}

public static void Argument(bool condition, string message, [CallerArgumentExpression("condition")] string conditionExpression = null)
{
    if (!condition) throw new ArgumentException(message: message, paramName: conditionExpression);
}

However, I cannot get the value of conditionExpression to be anything other than null.

I've been using this https://blog.mcilreavy.com/articles/2018-08/caller-argument-expression-attribute and a few other pages and, of course, good as a guide, but I can't get it to work.

[Not yet implemented](https://github.com/dotnet/csharplang/issues/287), not even in C# 9. — Jeroen Mostert, Nov 18 '20 at 20:30

RichardHowells · Accepted Answer · 2020-11-18T21:01:27.493

7

This page https://www.c-sharpcorner.com/article/c-sharp-8-features/ claims that it never made it to C#8 and is now C# Next.

See also https://github.com/dotnet/csharplang/issues/287 especially towards the bottom.

edited Nov 18 '20 at 21:01

answered Nov 18 '20 at 20:13

RichardHowells

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3

Looks like it's coming, in C# 10. (Circa November, so just weeks from now) – Sören Kuklau Sep 10 '21 at 14:49

score 2 · Answer 2 · answered Nov 12 '21 at 09:22

2

The feature was implemented in Roslyn compiler that supports C# 10, even if you are not using C# 10.

answered Nov 12 '21 at 09:22

Youssef13

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CallerArgumentExpression always null

2 Answers2

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