Docs: Surely this is not the latest syntax specification?

[PatrickRyder]

What about being able to test for null and declare a strong type in the same statement?

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Document Details

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• ID: 4bc2f58f-8fbc-9ff2-2312-8a5715536f1f
• Version Independent ID: 1dbd0d51-e1dc-8970-93f8-2a44fa71f7ba
• Content: as (C# Reference)
• Content Source: docs/csharp/language-reference/keywords/as.md
• Product: dotnet-csharp
• GitHub Login: @BillWagner
• Microsoft Alias: wiwagn

[BillWagner]

Thanks for pointing this out @PatrickRyder

I thought I had updated this page as part of the additions for pattern matching in C# 7. I clearly missed it.

What needs to be added:

• [ ] Using as with a strongly typed variable initializer.
• [ ] Using as with value types
• [ ] using as to perform null checking.~~

[pkulikov]

@BillWagner I'm confused. The following still produces compile error:

object a = 4;
var b = a as int;

@PatrickRyder did you mean the is expression, which is documented?
https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/is#pattern-matching-with-is
https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-7#is-expression

[PatrickRyder]

Hi, Petr,

I think I was getting confused with the is keyword. I was trying to find the new syntax for declaring a variable at the same time as testing it, e.g.:

if( sender is ComboBox myComboBox )
{
var item = myComboBox.SelectedItem;
}

My apologies.

*
Patrick

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From: Petr Kulikov [e-mail]
Sent: 11 October 2018 16:42
To: dotnet/docs
Cc: PatrickRyder; Mention
Subject: Re: [dotnet/docs] Surely this is not the latest syntax specification? (#8267)

@BillWagnerhttps://github.com/BillWagner I'm confused. The following still produces compile error:

object a = 4;
var b = a as int;

@PatrickRyderhttps://github.com/PatrickRyder did you mean the is expression, which is documented?
https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/is#pattern-matching-with-is
https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-7#is-expression

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[BillWagner]

@pkulikov sigh you're right. That's what I get for looking at something when my brain was totally focused on a different problem.

I hid my previous comment as resolved. (That seemed the best strategy).

One change that would be useful on the page for as: Add a new sentence at the beginning of the Remarks section something like:

The is expression can both test that a conversion will succeed and conditionally assign a variable when the conversion will succeed. In many scenarios, it is more concise than using the as operator.

The is above would be linked to the keyword for `is.

[pkulikov]

@PatrickRyder thanks for raising the issue. I don't think you are the only one who confuses as and is, especially given, how close those two in functionality and usage. As far as I remember, ReSharper suggests refactoring that converts as usage to the pattern matching with is. So, the addition suggested by @BillWagner is "in-field" and it's good it gets to the docs.