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c#: add LibraryImport source generator notes

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Marcello 2022-08-10 17:03:52 +02:00
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22
docs/dotnet/C#/C#.md
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@ -2913,7 +2913,7 @@ unsafe
} }
``` ```
### DllImport & Extern ### External Code
The `extern` modifier is used to declare a method that is implemented externally. The `extern` modifier is used to declare a method that is implemented externally.
A common use of the extern modifier is with the `DllImport` attribute when using Interop services to call into _unmanaged_ code. A common use of the extern modifier is with the `DllImport` attribute when using Interop services to call into _unmanaged_ code.
@ -2923,3 +2923,23 @@ In this case, the method must also be declared as `static`.
[DllImport("avifil32.dll")] [DllImport("avifil32.dll")]
private static extern void AVIFileInit(); private static extern void AVIFileInit();
``` ```
The `LibraryImport` attribute can be used to import external code and have the source generator handle the marshalling for the annotated function.
> **Note**: The source generator will still use the `DllImport` attribute in the generated code.
```cs
// before
public static class Native
{
[DllImport(nameof(Native), CharSet = CharSet.Unicode)]
public extern static string ToLower(string str);
}
// after
public static class Native
{
[LibraryImport(nameof(Native), StringMarshalling = StringMarshalling.Utf16)]
public static partial string ToLower(string str);
}
```