create "what's new in C# 7.3" #5448

BillWagner · 2018-05-17T18:46:36Z

This PR adds the overview to "What's new in C# 7.3". I updated the wording in the TOC to remove the repeated "What's new" phrasing.

/cc @jcouv @MadsTorgersen

/cc @Welchen

This PR relies on new files added in PR #5408

Summary

Describe your changes here.

Fixes #Issue_Number (if available)

jcouv · 2018-05-17T20:12:29Z

docs/csharp/whats-new/csharp-7-3.md

+
+- You can test `==` and `!=` with tuple types.
+- You can use expression variables in more locations.
+- You may attach attributes to the backing field of auto implemented properties.


Nit: auto-implemented

jcouv · 2018-05-17T20:12:59Z

docs/csharp/whats-new/csharp-7-3.md

+- You can use expression variables in more locations.
+- You may attach attributes to the backing field of auto implemented properties.
+- Method resolution when arguments differ by `in` has been improved.
+- Overload resolution new has fewer ambiguous cases.


Typo: new -> now

jcouv · 2018-05-17T20:14:16Z

docs/csharp/whats-new/csharp-7-3.md

+
+The new compiler options are:
+
+- `deterministic` to ensure that subsequent compilations of the same source generate the same binary output.


I'm surprised. "deterministic" is not a new option. It was there for a while.

Well, we got behind. I can move it to the correct version. Do you know when it was first added?

-deterministic was added in C# 6.0.

pkulikov · 2018-05-17T20:02:13Z

docs/csharp/whats-new/csharp-7-3.md

+---
+# What's new in C# 7.3
+
+There are two main themes to the C# 7.3 release. One theme provides features that enable safe code to be as performant as unsafe code. The second theme provides incremental improvements to existing features. In addition, new compilers were added in this release.


In the last sentence: ...new compilers... -> ...new compiler options...

pkulikov · 2018-05-17T20:03:58Z

docs/csharp/whats-new/csharp-7-3.md

+- You can reassign `ref` local variables.
+- You can use initializers on `stackalloc` arrays.
+- You can use `fixed` statements with any type that supports a pattern.
+- You can use additional generic constraints.


That one is on the border :). @BillWagner what made you put this in this theme and not in the theme of the enhancements to the existing features?

It could go in either section. I put it here because of the unmanaged constraint. That enables some more perf oriented generic programming.

OK, I see, thank you for the reply.

pkulikov · 2018-05-17T20:05:09Z

docs/csharp/whats-new/csharp-7-3.md

+- You can use expression variables in more locations.
+- You may attach attributes to the backing field of auto implemented properties.
+- Method resolution when arguments differ by `in` has been improved.
+- Overload resolution new has fewer ambiguous cases.


Overload resolution new... -> New overload resolution...?

"overload resolution now..."

pkulikov · 2018-05-17T20:06:05Z

docs/csharp/whats-new/csharp-7-3.md

+
+- `deterministic` to ensure that subsequent compilations of the same source generate the same binary output.
+- `publicsign` to enable OSS signing of assemblies.
+- `pathmap` to provide a mapping for source directories.


Should there be dashes in front of each compiler option?

pkulikov · 2018-05-17T20:13:10Z

docs/csharp/whats-new/csharp-7-3.md

+
+### Tuples support `==` and `!=`
+
+The C# tuple types now support `==` and `!=`. You can learn more about the rules in the article on [tuples](../tuples.md).


Consider to give the link to the section in that article: ../tuples.md#equality-and-tuples

pkulikov · 2018-05-17T20:19:18Z

docs/csharp/whats-new/csharp-7-3.md

+
+By default, every compilation unique output on each compilation. The compiler adds a timestamp, and a GUID generated from random numbers. You use this option if you want to compare the byte-for-byte output to ensure consistency across builds.
+
+For more information, see the [deterministic compiler option](../language-reference/compiler-options/deterministic-compiler-option.md) article.


nit: As far as I noticed, dashes are also used in the link texts throughout the docs.

pkulikov · 2018-05-17T20:19:35Z

docs/csharp/whats-new/csharp-7-3.md

+
+The `-publicsign` compiler option instructs the compiler to sign the assembly using a public key. The assembly is marked as signed, but the signature is taken from the public key. This option enables you to build signed assemblies from open-source projects using a public key.
+
+For more information, see the [publicsign compiler option](../language-reference/compiler-options/publicsign-compiler-option.md) article.


nit: dash in the link text

pkulikov · 2018-05-17T20:19:52Z

docs/csharp/whats-new/csharp-7-3.md

+
+The `-pathmap` compiler option instructs the compiler to replace source paths from the build environment with mapped source paths. The pathmap option controls the source path written by the compiler to PDB files or for the <xref:System.Runtime.CompilerServices.CallerFilePathAttribute>.
+
+For more information, see the [pathmap compiler option](../language-reference/compiler-options/pathmap-compile-option.md) article.


nit: dash in the link text

pkulikov · 2018-05-17T20:21:53Z

docs/csharp/whats-new/index.md

 * [C# 7.1](csharp-7-1.md):
-    - This page describes the features in C# 7.1. These features were added in [Visual Studio 2017 version 15.3](https://www.visualstudio.com/vs/whatsnew/), and in the [.NET Core 2.0 SDK](../../core/whats-new/index.md).
-
+  - This page describes the features in C# 7.1. These features were added in [Visual Studio 2017 version 15.3](https://www.visualstudio.com/vs/whatsnew/), and in the [.NET Core 2.0 SDK](../../core/whats-new/index.md).


The first sentence should be: This page describes the features added in C# 7.1.

pkulikov · 2018-05-17T20:22:20Z

docs/csharp/whats-new/index.md

 * [C# 7.2](csharp-7-2.md):
-    - This page describes the latest features in the C# language. C# 7.2 is currently available in [Visual Studio 2017 version 15.5](https://www.visualstudio.com/vs/whatsnew/), and in the [.NET Core 2.0 SDK](../../core/whats-new/index.md).
-
+  - This page describes the latest features in the C# language. C# 7.2 is currently available in [Visual Studio 2017 version 15.5](https://www.visualstudio.com/vs/whatsnew/), and in the [.NET Core 2.0 SDK](../../core/whats-new/index.md).


The first sentence should be: This page describes the features added in C# 7.2

jcouv

LGTM Thanks!

MihaMarkic · 2018-05-18T07:52:15Z

LGTM as well. Perhaps you could add a couple of enhancements:

add a Span<int> arr = stackalloc [] {1, 2, 3}; sample
add either Enum or Delegate or both samples to generic constraints

MihaMarkic · 2018-05-18T08:00:24Z

OTOH,

When the in argument modifier was added, these two methods would cause an ambiguity:

static void M(S arg);
static void M(in S arg);

Is this real? I've tested it with 7.2 and it works:

        static void X(int a) {}
        static void X(in int a) {}

BillWagner · 2018-05-18T15:32:04Z

Perhaps you could add a couple of enhancements:
add a Span arr = stackalloc [] {1, 2, 3}; sample

I like this idea. I added it.

add either Enum or Delegate or both samples to generic constraints

If want to keep this article reasonably short. The articles linked at the end of that section have samples of both Enum and Delegate, in addition to unmanaged.

BillWagner · 2018-05-18T15:33:17Z

Is this real? I've tested it with 7.2 and it works:

Yes, and I added a note that this is a bug fix, and the new resolution applies even if C# 7.2 is selected as the language version.

mairaw · 2018-05-18T23:55:40Z

docs/csharp/whats-new/index.md

+> The C# language relies on types and methods in a *standard library* for some of the features. One example is exception processing. Every `throw` statement or expression is checked to ensure the object being thrown is derived from <xref:System.Exception>. Similarly, every `catch` is checked to ensure that the type being caught is derived from <xref:System.Exception>. Each version may add new requirements. To use the latest language features in older environments, you may need to install specific libraries. These dependencies are documented in the page for each specific version. You can learn more about the [relationships between language and library](relationships-between-language-and-library.md) for background on this dependency.

+* [C# 7.3](csharp-7-3.md):
+  - This page describes the latest features in the C# language. C# 7.3 is currently available in [Visual Studio 2017 version 15.7](https://www.visualstudio.com/vs/whatsnew/), and in the [.NET Core 2.1 SDK Preview](../../core/whats-new/index.md).


2.1.300 RC1?

mairaw

Looks great @BillWagner. Left a couple of comments.

mairaw · 2018-05-18T23:57:02Z

docs/csharp/whats-new/csharp-7-3.md

+
+You can also use the new `unmanaged` constraint, to specify that a type parameter must be an **unmanaged type**. An **unmanaged type** is a type that isn't a reference type, and doesn't contain any reference type at any level of nesting.
+
+You can learn more in the articles on [`where` generic constraints](../language-reference/keywords/where-generic-type-constraints.md) and the article covering [constraints on type parameters](../programming-guide/generics/constraints-on-type-parameters.md).


there are a few broken links warnings like this one in the build report

I fixed this one. The others rely on #5408

mairaw · 2018-05-19T00:01:36Z

docs/csharp/whats-new/csharp-7-3.md

+
+You can learn more in the article on [`ref` returns and `ref` locals](../programming-guide/classes-and-structs/ref-returns.md).
+
+### `stackalloc` arrays support initializers


nit: I find it weird how the heading gets rendered when we use inline code. Wondering if it would be worth to ask them not to format inline code in headings while we still lock the word for Loc. Same applies to links.

I'm torn. I hate not styling them, because otherwise the first word should be caps. And the loc issue.

Keep the styling. My thought process was more related to UX changes. Like, should we work with @adkinn and co. to come up with some rules for when inline code should not be formatted like in headings and links?

mairaw · 2018-05-19T00:21:29Z

docs/csharp/whats-new/csharp-7-3.md

+
+You can now specify the type <xref:System.Enum?displayProperty=nameWithType> or <xref:System.Delegate?displayProperty=nameWithType> as base class constraints for a type parameter.
+
+You can also use the new `unmanaged` constraint, to specify that a type parameter must be an **unmanaged type**. An **unmanaged type** is a type that isn't a reference type, and doesn't contain any reference type at any level of nesting.


nit: remove comma from last sentence

mairaw · 2018-05-19T01:08:57Z

docs/csharp/whats-new/csharp-7-3.md

+
+### pathmap
+
+The `-pathmap` compiler option instructs the compiler to replace source paths from the build environment with mapped source paths. The pathmap option controls the source path written by the compiler to PDB files or for the <xref:System.Runtime.CompilerServices.CallerFilePathAttribute>.


inline code pathmap?

mairaw · 2018-05-19T01:12:23Z

docs/csharp/whats-new/csharp-7-3.md

+static void M(in S arg);
+```
+
+Now, the by value (first in the preceding example) overload is better than the by readonly reference version. To specify the by readonly reference version is called, you must include the `in` modifier when calling the method.


the first part of the last sentence is a bit hard to parse. Maybe if you change to something like "To call the by readonly reference version"?

mairaw · 2018-05-19T01:22:11Z

docs/csharp/whats-new/csharp-7-3.md

+
+```csharp
+var arr = new int[3] {1, 2, 3};
+var arr2 = new int[] { 1, 2, 3};


nit remove extra space

mairaw · 2018-05-19T01:22:29Z

docs/csharp/whats-new/csharp-7-3.md

+
+```csharp
+int* pArr = stackalloc int[3] {1, 2, 3};
+int* pArr2 = stackalloc int[] { 1, 2, 3};


nit remove extra space

mairaw · 2018-05-19T01:25:30Z

docs/csharp/whats-new/csharp-7-3.md

+
+### Extend expression variables in initializers
+
+The syntax added in C# 7.0 to permit out variable declarations has been extended to include field initializers, property initializers, constructor initializers, and query clauses. It enables code such as the following example:


replace permit with allow? inline code out?

mairaw · 2018-05-19T01:26:41Z

docs/csharp/whats-new/csharp-7-3.md

+
+## New compiler options
+
+New compiler options support new build and DevOps scenarios for C# programs


missing punctuation

mairaw · 2018-05-19T01:28:28Z

docs/csharp/whats-new/csharp-7-3.md

+
+The new compiler options are:
+
+- `-publicsign` to enable OSS signing of assemblies.


spell out OSS on first usage

pkulikov · 2018-05-21T15:40:43Z

docs/csharp/whats-new/csharp-7-3.md

 ### Tuples support `==` and `!=`

-The C# tuple types now support `==` and `!=`. You can learn more about the rules in the article on [tuples](../tuples.md#equality-and-tuples).
+The C# tuple types now support `==` and `!=`. Fore more information, see the section covering [equality](../tuples.md#equality-and-tuples) in the article on [tuples](../tuples.md#equality-and-tuples).


nit: the sentence should end with the link to the article itself, not the section:
...in the article on [tuples](../tuples.md)

pkulikov · 2018-05-21T15:41:34Z

docs/csharp/whats-new/csharp-7-3.md

 ### Extend expression variables in initializers

-The syntax added in C# 7.0 to permit out variable declarations has been extended to include field initializers, property initializers, constructor initializers, and query clauses. It enables code such as the following example:
+The syntax added in C# 7.0 to aloow `out` variable declarations has been extended to include field initializers, property initializers, constructor initializers, and query clauses. It enables code such as the following example:


Typo: aloow -> allow

pkulikov · 2018-05-21T15:42:22Z

docs/csharp/whats-new/csharp-7-3.md

 ### pathmap

-The `-pathmap` compiler option instructs the compiler to replace source paths from the build environment with mapped source paths. The pathmap option controls the source path written by the compiler to PDB files or for the <xref:System.Runtime.CompilerServices.CallerFilePathAttribute>.
+The `-pathmap` compiler option instructs the compiler to replace source paths from the build environment with mapped source paths. The `pathmap` option controls the source path written by the compiler to PDB files or for the <xref:System.Runtime.CompilerServices.CallerFilePathAttribute>.


nit: add dash to the second mention of -pathmap

BillWagner · 2018-05-23T17:08:18Z

closing and reopening to start a new build.

svick · 2018-05-25T10:31:39Z

docs/csharp/whats-new/csharp-7-3.md

+}
+```
+
+The variable `p` doesn't need to be pinned. Note that you still need an `unsafe` context. In earlier versions of C#, you need to declare a second fixed pointer:


I think it's inaccurate to say that p doesn't need to be pinned. p is just an int, it can't be pinned and the following example does not pin p.

svick · 2018-05-25T10:34:03Z

docs/csharp/whats-new/csharp-7-3.md

+    public void M()
+    {
+        int p = s.myFixedField[5];
+    }


As the following text says, this code has be in an unsafe context, so I think this example should include unsafe somewhere (probably on the method).

svick · 2018-05-25T10:42:41Z

docs/csharp/whats-new/csharp-7-3.md

+
+```csharp
+ref VeryLargeStruct reflocal = ref veryLargeStruct; // initialization
+refLocal = ref anotherVeryLargeStruct; // reassigned, refLocal refers to different storage.


Typo: first line uses reflocal (with lowecase l), second line refLocal (with capital L).

mairaw · 2018-05-25T18:48:12Z

There are some build warnings here, @BillWagner. I'll take a look at the rest now.

mairaw

LGTM. @svick had some new comments you might wanna check and you still have one instance of OSS which is not spelled out. You can use the acronym after you show what it means once.

@jcouv

Fixes #5289 This PR adds the overview to "What's new in C# 7.3". I updated the wording in the TOC to remove the repeated "What's new" phrasing. /cc @jcouv @MadsTorgersen /cc @Welchen This PR relies on new files added in PR #5408

compile => compiler.

jcouv · 2018-05-30T04:58:58Z

docs/csharp/whats-new/csharp-7-3.md

+Now, `ref` locals may be reassigned to refer to different instances after being initialized. The following code now compiles:
+
+```csharp
+ref VeryLargeStruct refLocal = ref veryLargeStruct; // initialization


There is one more form of ref local re-assignment: foreach ref. It was missing from the spec, but it is implemented and shipped.

using System; class E { public class Enumerator { public ref int Current => throw new NotImplementedException(); public bool MoveNext() => throw new NotImplementedException(); } public Enumerator GetEnumerator() => new Enumerator(); } class C { void M() { foreach (ref int x in new E()) { } } }

[I'd given a bad example. Updated]

@jcouv that means we can make such shoot-in-the-leg things now:

var _array = new byte[5]; new Random(42).NextBytes(_array); Span<byte> span = _array; foreach (ref byte element in span) { element = 4; Console.WriteLine(element); } Console.WriteLine(string.Join(" ", _array)); Console.ReadLine();

That outputs only 4s. Wow.

BillWagner requested review from jcouv, mairaw and rpetrusha May 17, 2018 18:46

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Confused about v 7.3 dotnet/csharplang#1516

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BillWagner and others added 5 commits May 25, 2018 15:59

create "what's new in C# 7.3"

d1dcc14

Fixes #5289 This PR adds the overview to "What's new in C# 7.3". I updated the wording in the TOC to remove the repeated "What's new" phrasing. /cc @jcouv @MadsTorgersen /cc @Welchen This PR relies on new files added in PR #5408

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BillWagner force-pushed the whats-new-in-csharp branch from 469998f to e5e4ce1 Compare May 25, 2018 20:01

fix a build error

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compile => compiler.

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C# 7.3: Include foreach loop variables in ref reassignment #5707

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		The new compiler options are:

		- `deterministic` to ensure that subsequent compilations of the same source generate the same binary output.


		### Tuples support `==` and `!=`

		The C# tuple types now support `==` and `!=`. You can learn more about the rules in the article on [tuples](../tuples.md).


		By default, every compilation unique output on each compilation. The compiler adds a timestamp, and a GUID generated from random numbers. You use this option if you want to compare the byte-for-byte output to ensure consistency across builds.

		For more information, see the [deterministic compiler option](../language-reference/compiler-options/deterministic-compiler-option.md) article.


		The `-publicsign` compiler option instructs the compiler to sign the assembly using a public key. The assembly is marked as signed, but the signature is taken from the public key. This option enables you to build signed assemblies from open-source projects using a public key.

		For more information, see the [publicsign compiler option](../language-reference/compiler-options/publicsign-compiler-option.md) article.


		The `-pathmap` compiler option instructs the compiler to replace source paths from the build environment with mapped source paths. The pathmap option controls the source path written by the compiler to PDB files or for the <xref:System.Runtime.CompilerServices.CallerFilePathAttribute>.

		For more information, see the [pathmap compiler option](../language-reference/compiler-options/pathmap-compile-option.md) article.


		You can also use the new `unmanaged` constraint, to specify that a type parameter must be an unmanaged type. An unmanaged type is a type that isn't a reference type, and doesn't contain any reference type at any level of nesting.

		You can learn more in the articles on [`where` generic constraints](../language-reference/keywords/where-generic-type-constraints.md) and the article covering [constraints on type parameters](../programming-guide/generics/constraints-on-type-parameters.md).


		You can learn more in the article on [`ref` returns and `ref` locals](../programming-guide/classes-and-structs/ref-returns.md).

		### `stackalloc` arrays support initializers


		You can now specify the type <xref:System.Enum?displayProperty=nameWithType> or <xref:System.Delegate?displayProperty=nameWithType> as base class constraints for a type parameter.

		You can also use the new `unmanaged` constraint, to specify that a type parameter must be an unmanaged type. An unmanaged type is a type that isn't a reference type, and doesn't contain any reference type at any level of nesting.


		### pathmap

		The `-pathmap` compiler option instructs the compiler to replace source paths from the build environment with mapped source paths. The pathmap option controls the source path written by the compiler to PDB files or for the <xref:System.Runtime.CompilerServices.CallerFilePathAttribute>.


		### Extend expression variables in initializers

		The syntax added in C# 7.0 to permit out variable declarations has been extended to include field initializers, property initializers, constructor initializers, and query clauses. It enables code such as the following example:


		## New compiler options

		New compiler options support new build and DevOps scenarios for C# programs


		The new compiler options are:

		- `-publicsign` to enable OSS signing of assemblies.

create "what's new in C# 7.3" #5448

create "what's new in C# 7.3" #5448

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