New in csharp7 (dotnet#1188)

* Create What's new in C# 7 content

* fix a merge mistake.

* update per editorial feedback.

* Fixing OPS build

* address review comments.

From @jaredpar

.gitattributes

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+###############################################################################
+# Set default behavior to automatically normalize line endings.
+###############################################################################
+* text=auto
+
+###############################################################################
+# Set default behavior for command prompt diff.
+#
+# This is need for earlier builds of msysgit that does not have it on by
+# default for csharp files.
+# Note: This is only used by command line
+###############################################################################
+#*.cs     diff=csharp
+
+###############################################################################
+# Set the merge driver for project and solution files
+#
+# Merging from the command prompt will add diff markers to the files if there
+# are conflicts (Merging from VS is not affected by the settings below, in VS
+# the diff markers are never inserted). Diff markers may cause the following 
+# file extensions to fail to load in VS. An alternative would be to treat
+# these files as binary and thus will always conflict and require user
+# intervention with every merge. To do so, just uncomment the entries below
+###############################################################################
+#*.sln       merge=binary
+#*.csproj    merge=binary
+#*.vbproj    merge=binary
+#*.vcxproj   merge=binary
+#*.vcproj    merge=binary
+#*.dbproj    merge=binary
+#*.fsproj    merge=binary
+#*.lsproj    merge=binary
+#*.wixproj   merge=binary
+#*.modelproj merge=binary
+#*.sqlproj   merge=binary
+#*.wwaproj   merge=binary
+
+###############################################################################
+# behavior for image files
+#
+# image files are treated as binary by default.
+###############################################################################
+#*.jpg   binary
+#*.png   binary
+#*.gif   binary
+
+###############################################################################
+# diff behavior for common document formats
+# 
+# Convert binary document formats to text before diffing them. This feature
+# is only available from the command line. Turn it on by uncommenting the 
+# entries below.
+###############################################################################
+#*.doc   diff=astextplain
+#*.DOC   diff=astextplain
+#*.docx  diff=astextplain
+#*.DOCX  diff=astextplain
+#*.dot   diff=astextplain
+#*.DOT   diff=astextplain
+#*.pdf   diff=astextplain
+#*.PDF   diff=astextplain
+#*.rtf   diff=astextplain
+#*.RTF   diff=astextplain

samples/snippets/csharp/new-in-7/new-in-7.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio 15
+VisualStudioVersion = 15.0.25807.0
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "new-in-7", "new-in-7\new-in-7.csproj", "{63DBE099-DB24-4607-A930-FFEE506CE84C}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{63DBE099-DB24-4607-A930-FFEE506CE84C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{63DBE099-DB24-4607-A930-FFEE506CE84C}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{63DBE099-DB24-4607-A930-FFEE506CE84C}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{63DBE099-DB24-4607-A930-FFEE506CE84C}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+EndGlobal

samples/snippets/csharp/new-in-7/new-in-7/App.config

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+<?xml version="1.0" encoding="utf-8" ?>
+<configuration>
+    <startup> 
+        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5.2" />
+    </startup>
+</configuration>

samples/snippets/csharp/new-in-7/new-in-7/AsyncWork.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace new_in_7
+{
+    public class AsyncWork
+    {
+        #region 29_TaskExample
+        public Task<string> PerformLongRunningWork(string address, int index, string name)
+        {
+            if (string.IsNullOrWhiteSpace(address))
+                throw new ArgumentException(message: "An address is required", paramName: nameof(address));
+            if (index < 0)
+                throw new ArgumentOutOfRangeException(paramName: nameof(index), message: "The index must be non-negative");
+            if (string.IsNullOrWhiteSpace(name))
+                throw new ArgumentException(message: "You must supply a name", paramName: nameof(name));
+
+            return longRunningWorkImplementation();
+
+            async Task<string> longRunningWorkImplementation()
+            {
+                var interimResult = await FirstWork(address);
+                var secondResult = await SecondStep(index, name);
+                return $"The results are {interimResult} and {secondResult}. Enjoy.";
+            }
+        }
+        #endregion
+
+        private async Task<string> SecondStep(Int32 index, String name)
+        {
+            await Task.Delay(50);
+            return "This could be a format string";
+        }
+
+        private async Task<int> FirstWork(String address)
+        {
+            await Task.Delay(100);
+            return 42;
+        }
+
+        #region 36_TaskLambdaExample
+        public Task<string> PerformLongRunningWorkLambda(string address, int index, string name)
+        {
+            if (string.IsNullOrWhiteSpace(address))
+                throw new ArgumentException(message: "An address is required", paramName: nameof(address));
+            if (index < 0)
+                throw new ArgumentOutOfRangeException(paramName: nameof(index), message: "The index must be non-negative");
+            if (string.IsNullOrWhiteSpace(name))
+                throw new ArgumentException(message: "You must supply a name", paramName: nameof(name));
+
+            Func<Task<string>> longRunningWorkImplementation = async () =>
+            {
+                var interimResult = await FirstWork(address);
+                var secondResult = await SecondStep(index, name);
+                return $"The results are {interimResult} and {secondResult}. Enjoy.";
+            };
+
+            return longRunningWorkImplementation();
+        }
+        #endregion
+
+        #region 30_UsingValueTask
+        public async ValueTask<int> Func()
+        {
+            await Task.Delay(100);
+            return 5;
+        }
+        #endregion
+
+        #region 31_AsyncOptimizedValueTask
+        public ValueTask<int> CachedFunc()
+        {
+            return (cache) ? new ValueTask<int>(cacheResult) : new ValueTask<int>(loadCache());
+        }
+        private bool cache = false;
+        private int cacheResult;
+        private async Task<int> loadCache()
+        {
+            // simulate async work:
+            await Task.Delay(100);
+            cache = true;
+            cacheResult = 100;
+            return cacheResult;
+        }
+        #endregion
+
+    }
+}

samples/snippets/csharp/new-in-7/new-in-7/Iterator.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace new_in_7
+{
+    public static class Iterator
+    {
+        #region 25_IteratorMethod
+        public static IEnumerable<char> AlphabetSubset(char start, char end)
+        {
+            if ((start < 'a') || (start > 'z'))
+                throw new ArgumentOutOfRangeException(paramName: nameof(start), message: "start must be a letter");
+            if ((end < 'a') || (end > 'z'))
+                throw new ArgumentOutOfRangeException(paramName: nameof(end), message: "end must be a letter");
+
+            if (end <= start)
+                throw new ArgumentException($"{nameof(end)} must be greater than {nameof(start)}");
+            for (var c = start; c < end; c++)
+                yield return c;
+        }
+        #endregion
+
+        #region 27_IteratorMethodRefactored
+        public static IEnumerable<char> AlphabetSubset2(char start, char end)
+        {
+            if ((start < 'a') || (start > 'z'))
+                throw new ArgumentOutOfRangeException(paramName: nameof(start), message: "start must be a letter");
+            if ((end < 'a') || (end > 'z'))
+                throw new ArgumentOutOfRangeException(paramName: nameof(end), message: "end must be a letter");
+
+            if (end <= start)
+                throw new ArgumentException($"{nameof(end)} must be greater than {nameof(start)}");
+            return alphabetSubsetImplementation(start, end);
+        }
+
+        private static IEnumerable<char> alphabetSubsetImplementation(char start, char end)
+        { 
+            for (var c = start; c < end; c++)
+                yield return c;
+        }
+        #endregion
+
+        #region 28_IteratorMethodLocal
+        public static IEnumerable<char> AlphabetSubset3(char start, char end)
+        {
+            if ((start < 'a') || (start > 'z'))
+                throw new ArgumentOutOfRangeException(paramName: nameof(start), message: "start must be a letter");
+            if ((end < 'a') || (end > 'z'))
+                throw new ArgumentOutOfRangeException(paramName: nameof(end), message: "end must be a letter");
+
+            if (end <= start)
+                throw new ArgumentException($"{nameof(end)} must be greater than {nameof(start)}");
+
+            return alphabetSubsetImplementation();
+
+            IEnumerable<char> alphabetSubsetImplementation()
+            {
+                for (var c = start; c < end; c++)
+                    yield return c;
+            }
+        }
+        #endregion
+
+    }
+}

samples/snippets/csharp/new-in-7/new-in-7/MathUtilities.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace new_in_7
+{
+    public static class MathUtilities
+    {
+        #region 37_LocalFunctionFactorial
+        public static int LocalFunctionFactorial(int n)
+        {
+            return nthFactorial(n);
+            int nthFactorial(int number) => (number < 2) ? 
+                1 : number * nthFactorial(number - 1);
+        }
+        #endregion
+
+        #region 38_LambdaFactorial
+        public static int LambdaFactorial(int n)
+        {
+            Func<int, int> nthFactorial = default(Func<int, int>);
+            nthFactorial = (number) => (number < 2) ? 
+                1 : number * nthFactorial(number - 1);
+            return nthFactorial(n);
+        }
+        #endregion
+    }
+}

samples/snippets/csharp/new-in-7/new-in-7/MatrixSearch.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace new_in_7
+{
+    static class MatrixSearch
+    {
+        #region 20_FindReturningIndices
+        public static (int i, int j) Find(int[,] matrix, Func<int, bool> predicate)
+        {
+            for (int i = 0; i < matrix.GetLength(0); i++)
+                for (int j = 0; j < matrix.GetLength(1); j++)
+                    if (predicate(matrix[i, j]))
+                        return (i, j);
+            return (-1, -1); // Not found
+        }
+        #endregion
+
+        #region 22_FindReturningRef
+        public static ref int Find3(int[,] matrix, Func<int, bool> predicate)
+        {
+            for (int i = 0; i < matrix.GetLength(0); i++)
+                for (int j = 0; j < matrix.GetLength(1); j++)
+                    if (predicate(matrix[i, j]))
+                        return ref matrix[i, j];
+            throw new InvalidOperationException("Not found");
+        }
+        #endregion
+    }
+}

samples/snippets/csharp/new-in-7/new-in-7/Point.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace new_in_7
+{
+    #region 11_PointWithDeconstruction
+    public class Point
+    {
+        public Point(double x, double y)
+        {
+            this.X = x;
+            this.Y = y;
+        }
+
+        public double X { get; }
+        public double Y { get; }
+
+        public void Deconstruct(out double x, out double y)
+        {
+            x = this.X;
+            y = this.Y;
+        }
+    }
+    #endregion
+}