Use ReadOnlySpan where possible (#46344)

Author: gewarren

docs/fundamentals/runtime-libraries/snippets/System/Span/Overview/csharp/Program2.cs

@@ -5,15 +5,16 @@ class Program2
     static void Run()
     {
         string contentLength = "Content-Length: 132";
-        var length = GetContentLength(contentLength.ToCharArray());
+        int length = GetContentLength(contentLength.ToCharArray());
         Console.WriteLine($"Content length: {length}");
     }
 
     private static int GetContentLength(ReadOnlySpan<char> span)
     {
-        var slice = span.Slice(16);
+        ReadOnlySpan<char> slice = span.Slice(16);
         return int.Parse(slice);
     }
 }
+
 // Output:
 //      Content length: 132

docs/fundamentals/runtime-libraries/snippets/System/Span/Overview/csharp/Project.csproj

@@ -1,8 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <OutputType>Library</OutputType>
-    <TargetFrameworks>net8</TargetFrameworks>
+    <OutputType>Exe</OutputType>
+    <TargetFrameworks>net9</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
 

docs/fundamentals/runtime-libraries/snippets/System/Span/Overview/csharp/program.cs

@@ -20,18 +20,19 @@ private static void CreateSpanFromArray()
     {
         // <Snippet1>
         // Create a span over an array.
-        var array = new byte[100];
-        var arraySpan = new Span<byte>(array);
+        byte[] array = new byte[100];
+        Span<byte> arraySpan = new(array);
 
         byte data = 0;
         for (int ctr = 0; ctr < arraySpan.Length; ctr++)
             arraySpan[ctr] = data++;
 
         int arraySum = 0;
-        foreach (var value in array)
+        foreach (byte value in array)
             arraySum += value;
 
         Console.WriteLine($"The sum is {arraySum}");
+
         // Output:  The sum is 4950
         // </Snippet1>
     }
@@ -40,7 +41,7 @@ private static void CreateSpanFromNativeMemory()
     {
         // <Snippet2>
         // Create a span from native memory.
-        var native = Marshal.AllocHGlobal(100);
+        nint native = Marshal.AllocHGlobal(100);
         Span<byte> nativeSpan;
         unsafe
         {
@@ -51,11 +52,12 @@ private static void CreateSpanFromNativeMemory()
             nativeSpan[ctr] = data++;
 
         int nativeSum = 0;
-        foreach (var value in nativeSpan)
+        foreach (byte value in nativeSpan)
             nativeSum += value;
 
         Console.WriteLine($"The sum is {nativeSum}");
         Marshal.FreeHGlobal(native);
+
         // Output:  The sum is 4950
         // </Snippet2>
     }
@@ -70,10 +72,11 @@ private static void CreateSpanFromStack()
             stackSpan[ctr] = data++;
 
         int stackSum = 0;
-        foreach (var value in stackSpan)
+        foreach (byte value in stackSpan)
             stackSum += value;
 
         Console.WriteLine($"The sum is {stackSum}");
+
         // Output:  The sum is 4950
         // </Snippet3>
     }
@@ -85,8 +88,8 @@ public class ProgramB
     public static void WorkWithSpans()
     {
         // Create a span over an array.
-        var array = new byte[100];
-        var arraySpan = new Span<byte>(array);
+        byte[] array = new byte[100];
+        Span<byte> arraySpan = new(array);
 
         InitializeSpan(arraySpan);
         Console.WriteLine($"The sum is {ComputeSum(arraySpan):N0}");
@@ -118,14 +121,15 @@ public static void InitializeSpan(Span<byte> span)
             span[ctr] = value++;
     }
 
-    public static int ComputeSum(Span<byte> span)
+    public static int ComputeSum(ReadOnlySpan<byte> span)
     {
         int sum = 0;
-        foreach (var value in span)
+        foreach (byte value in span)
             sum += value;
 
         return sum;
     }
+
     // The example displays the following output:
     //    The sum is 4,950
     //    The sum is 4,950

docs/fundamentals/runtime-libraries/system-span{t}.md

@@ -1,7 +1,7 @@
 ---
 title: System.Span<T> struct
 description: Learn about the System.Span\<T> struct.
-ms.date: 12/31/2023
+ms.date: 05/21/2025
 dev_langs:
   - CSharp
   - FSharp
@@ -34,7 +34,7 @@ The following example uses the C# [stackalloc](/dotnet/csharp/language-reference
 :::code language="csharp" source="./snippets/System/Span/Overview/csharp/program.cs" id="Snippet3":::
 :::code language="fsharp" source="./snippets/System/Span/Overview/fsharp/program.fs" id="Snippet3":::
 
-Because `Span<T>` is an abstraction over an arbitrary block of memory, methods of the `Span<T>` type and methods with `Span<T>` parameters operate on any `Span<T>` object regardless of the kind of memory it encapsulates. For example, each of the separate sections of code that initialize the span and calculate the sum of its elements can be changed into single initialization and calculation methods, as the following example illustrates:
+Because `Span<T>` is an abstraction over an arbitrary block of memory, methods of the `Span<T>` type and methods with `Span<T>` parameters operate on any `Span<T>` object regardless of the kind of memory it encapsulates. For example, each of the separate sections of code that initialize the span and calculate the sum of its elements can be refactored into single initialization and calculation methods, as the following example illustrates:
 
 :::code language="csharp" source="./snippets/System/Span/Overview/csharp/program.cs" id="Snippet4":::
 :::code language="fsharp" source="./snippets/System/Span/Overview/fsharp/program.fs" id="Snippet4":::