Why is `Memory<T>` parameter access restricted only in `void`-returning method?

### Type of issue

Typo

### Description

From https://learn.microsoft.com/en-us/dotnet/standard/memory-and-spans/memory-t-usage-guidelines#usage-guidelines

> Rule #3: If your method accepts Memory and returns void, you must not use the Memory instance after your method returns.

```csharp
// !!! INCORRECT IMPLEMENTATION !!!
static void Log(ReadOnlyMemory message)
{
// Run in background so that we don't block the main thread while performing IO.
Task.Run(() =>
{
StreamWriter sw = File.AppendText(@".\input-numbers.dat");
sw.WriteLine(message);
});
}
```

Consult similar implimentation

```csharp
static int Log(ReadOnlyMemory message)
{

var length = message.Length;
if (length == 0)
{
return 0;
}

Task.Run(() =>
{
StreamWriter sw = File.AppendText(@".\input-numbers.dat");
sw.WriteLine(message);
});

return length;
}
```

This method is `int` returning and it violates same rule. It acceses `Memory` parameter after it returned.

#3 is not related to return type but to fact that method is synchronous. Problem is that synchronous method sets up execution that accesses buffer after it returns.

### Page URL

https://learn.microsoft.com/en-us/dotnet/standard/memory-and-spans/memory-t-usage-guidelines

### Content source URL

https://github.com/dotnet/docs/blob/main/docs/standard/memory-and-spans/memory-t-usage-guidelines.md

### Document Version Independent Id

d6cf8d26-fb2f-7138-f0c7-ab529a5b9cde

### Article author

@gewarren

### Metadata

* ID: 4819512e-1044-1c57-0de1-447164220fd5
* Service: **dotnet-fundamentals**