Null billion dollar

Author: rstropek

NullBillionDollar/NullBillionDollar.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.4.32916.344
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "NullBillionDollar", "NullBillionDollar\NullBillionDollar.csproj", "{7E148EA3-B286-4E7B-BDAF-C41D80A4F1DB}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{7E148EA3-B286-4E7B-BDAF-C41D80A4F1DB}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{7E148EA3-B286-4E7B-BDAF-C41D80A4F1DB}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{7E148EA3-B286-4E7B-BDAF-C41D80A4F1DB}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{7E148EA3-B286-4E7B-BDAF-C41D80A4F1DB}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {C7B1C2E4-EA1E-4F83-9441-3E2B678EA7E4}
+	EndGlobalSection
+EndGlobal

NullBillionDollar/NullBillionDollar/NullBillionDollar.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>Exe</OutputType>
+        <TargetFramework>net7.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <LangVersion>preview</LangVersion>
+    </PropertyGroup>
+
+</Project>

NullBillionDollar/NullBillionDollar/Program.cs

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+#nullable enable
+using System.Text.Json;
+using System.Text.Json.Nodes;
+
+// Null check in functions
+DoSomething("Hello");
+static void DoSomething(string? s)
+{
+    ArgumentNullException.ThrowIfNull(s);
+}
+
+// Null coalescing operator
+Console.WriteLine(IntoNotNull(null));
+Console.WriteLine(MultipleIntoNotNull(null, "FooBar"));
+static string IntoNotNull(string? maybeNullString) => maybeNullString ?? "default";
+static string MultipleIntoNotNull(string? maybeNullString, string? second)
+    => maybeNullString ?? second ?? "default";
+
+// Null coalescing operator with throw expression
+Console.WriteLine(ThrowIfNull("FooBar"));
+static string ThrowIfNull(string? maybeNullString) => maybeNullString ?? throw new ArgumentNullException(null, nameof(maybeNullString));
+
+ThrowIfNullStatement("FooBar");
+static void ThrowIfNullStatement(string? maybeNullString) => _ = maybeNullString ?? throw new ArgumentNullException(null, nameof(maybeNullString));
+
+// Null coalescing assignment operator
+List<int>? numbers = null;
+Push(42);
+Push(43);
+Console.WriteLine(JsonSerializer.Serialize(numbers));
+void Push(int number)
+{
+    numbers ??= new List<int>();
+    numbers.Add(number);
+}
+
+Console.WriteLine(GetNameOfHero(42));
+Console.WriteLine(GetNameOfHero(44));
+string GetNameOfHero(int id)
+{
+    var heroes = JsonNode.Parse("""
+        {
+            "theBoys": [
+                { "id": 42, "name": "Starlight", "canFly": false },
+                { "id": 43, "name": "Homelander", "canFly": true }
+            ]
+        }
+        """);
+
+    var theBoys = heroes?["theBoys"] as JsonArray;
+    //                                     +---- Null conditional indexer
+    //                                     |       +---- Null conditional operator
+    //                                     |       |                  +---- Null coalescing operator
+    //                                     v       v                  v
+    return theBoys?.FirstOrDefault(b => ((b?["id"])?.GetValue<int?>() ?? -1) == id)?["name"]?.GetValue<string?>() ?? "not found";
+}
+
+Console.WriteLine(GetNameOfHeroForgiving(42));
+Console.WriteLine(GetNameOfHeroForgiving(44));
+string GetNameOfHeroForgiving(int id)
+{
+    var heroes = JsonNode.Parse("""
+        {
+            "theBoys": [
+                { "id": 42, "name": "Starlight", "canFly": false },
+                { "id": 43, "name": "Homelander", "canFly": true }
+            ]
+        }
+        """);
+
+    var theBoys = heroes!["theBoys"] as JsonArray;
+
+    // Assumption: We KNOW that theBoys is not null and that properties id and name exist
+    // -> We can use the ! operator to tell the compiler that we know what we are doing
+    return theBoys!.FirstOrDefault(b => (b!["id"])!.GetValue<int>() == id)?["name"]!.GetValue<string?>() ?? "not found";
+}
+
+Console.WriteLine(NullPattern1(null));
+string NullPattern1(string? input)
+{
+    // Note: Null pattern ignores overloads of == operator
+    if (input is null)
+    {
+        return "default";
+    }
+
+    return input;
+}
+
+Console.WriteLine(NullPattern2(null));
+string NullPattern2(string? input)
+{
+    if (input is not null)
+    {
+        return input;
+    }
+
+    return "default";
+}