Clean edit pass on attributes #44513
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| title: "Attributes interpreted by the compiler: Pseudo-attributes" | ||
| ms.date: 01/2/2025 | ||
| description: "Learn about attributes you can add to code that are written to IL as modifiers. These custom attributes aren't emitted as attributes in the compiled output." | ||
| --- | ||
| # Custom attributes that generate flags or options in the Intermediate Language (IL) output | ||
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| You add these attributes to your code for the compiler to emit a specified Intermediate Language (IL) modifier. These attributes instruct the compiler to include the corresponding IL modifier in the output. | ||
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| | Attribute | Modifier | Comments | | ||
| |--------------------------------------------------------------------------------------|-----------------|-----------| | ||
| | <xref:System.Runtime.InteropServices.ComImportAttribute?displayProperty=fullName> | `import` | | | ||
| | <xref:System.Runtime.InteropServices.DllImportAttribute?displayProperty=fullName> | `pinvokeimpl` | You can add options listed in the constructor. | | ||
| | <xref:System.Runtime.InteropServices.FieldOffsetAttribute?displayProperty=fullName> | `.field` | This sets the field offset for memory layout. | | ||
| | <xref:System.Runtime.InteropServices.MarshalAsAttribute> | `marshal` | You can set options listed in the constructor. | | ||
| | <xref:System.Runtime.CompilerServices.MethodImplAttribute?displayProperty=fullName> | `flag` | Constructor arguments specify specific named flags such as `aggressiveinlining` or `forwardref`. These flags also specify the `native`, `managed`, or `optil` modifiers for the <xref:System.Runtime.CompilerServices.MethodCodeType?displayProperty=fullName> field. | | ||
| | <xref:System.NonSerializedAttribute?displayProperty=fullName> | `notserialized` | | | ||
| | <xref:System.Runtime.InteropServices.OptionalAttribute?displayProperty=fullName> | `[opt]` | | | ||
| | <xref:System.Runtime.InteropServices.OutAttribute?displayProperty=fullName> | `[out]` | | | ||
| | <xref:System.Runtime.InteropServices.PreserveSigAttribute?displayProperty=fullName> | `preservesig` | | | ||
| | <xref:System.SerializableAttribute?displayProperty=fullName> | `serializable` | | | ||
| | <xref:System.Runtime.InteropServices.StructLayoutAttribute?displayProperty=fullName> | `auto`, `sequential`, or `explicit` | Layout options can be set using the parameters. | | ||
| | <xref:System.Runtime.CompilerServices.IndexerNameAttribute?displayProperty=fullName> | | You add this attribute to an indexer to set a different method name. By default, indexers are compiled to a property named `Item`. You can specify a different name using this attribute. | | ||
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| Some of these custom attributes are applied using other C# syntax rather than adding the attribute to your source code. | ||
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| | Attribute | Comments | | ||
| |--------------------------------------------------------------------------------------------------|----------| | ||
| | <xref:System.Runtime.InteropServices.DefaultParameterValueAttribute?displayProperty=fullName> | Specifies the default value for the parameter. Use the [default parameter syntax](../../methods.md#optional-parameters-and-arguments). | | ||
| | <xref:System.Runtime.InteropServices.InAttribute?displayProperty=fullName> | Specifies the IL `[in]` modifier. Use the [`in`](../keywords/method-parameters.md#in-parameter-modifier) or [`ref readonly`](../keywords/method-parameters.md#ref-readonly-modifier). | | ||
| | <xref:System.Runtime.CompilerServices.SpecialNameAttribute?displayProperty=fullName> | Specifies the IL `specialname` modifier. The compiler automatically adds this modifier for methods that require it. | | ||
| | <xref:System.Runtime.InteropServices.UnmanagedCallersOnlyAttribute?displayProperty=nameWithType> | This attribute is required for the `delegate*` feature. The compiler adds it to any [`delegate*`](../unsafe-code.md#function-pointers) that requires its use. | | ||
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There was a problem hiding this comment.
using System.Runtime.InteropServices;
unsafe
{
delegate* unmanaged<void> someFuncPointer = &SomeMethod;
}
[UnmanagedCallersOnly] // Compilation fails if this is removed
static void SomeMethod() { } |
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| The following custom attributes are generally disallowed in C# source. They're listed here to aid library authors who use reflection, and to ensure you don't create custom attributes with the same name. | ||
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There was a problem hiding this comment. Though, creating custom attributes with the same name in a different namespace is okay, and custom attributes don't go in the System namespace. |
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| | Attribute | Comments | | ||
| |--------------------------------------------------------------------------------------------------|---------| | ||
| | <xref:System.Runtime.CompilerServices.CompilerFeatureRequiredAttribute?displayProperty=fullName> | Prevents downlevel compilers from using metadata it can't safely understand. | | ||
| | <xref:System.Runtime.CompilerServices.DecimalConstantAttribute?displayProperty=fullName> | Encodes `const decimal` fields. The runtime doesn't support `decimal` values as constant values. | | ||
| | <xref:System.Reflection.DefaultMemberAttribute?displayProperty=fullName> | Encodes indexers with <xref:System.Runtime.CompilerServices.IndexerNameAttribute?displayProperty=fullName>. This attribute notes the default indexer when its name is different than `Item`. This attribute is allowed in source. | | ||
| | <xref:System.Runtime.CompilerServices.DynamicAttribute?displayProperty=fullName> | Encodes whether a type in a signature is `dynamic` (versus `object`). | | ||
| | <xref:System.Runtime.CompilerServices.ExtensionAttribute?displayProperty=fullName> | This attribute notes extension methods. The compiler also places this attribute on the containing classes. | | ||
| | <xref:System.Runtime.CompilerServices.FixedBufferAttribute?displayProperty=fullName> | This attribute specifies `fixed` struct fields. | | ||
| | <xref:System.Runtime.CompilerServices.IsByRefLikeAttribute?displayProperty=fullName> | This attribute specifies a `ref` struct. | | ||
| | <xref:System.Runtime.CompilerServices.IsReadOnlyAttribute?displayProperty=fullName> | This attribute indicates that a parameter has the `in` modifier. It distinguishes `in` parameters from `readonly ref` or `[In] ref`. | | ||
| | <xref:System.Runtime.CompilerServices.RequiresLocationAttribute?displayProperty=fullName> | This attribute indicates that a parameter has the `readonly ref` modifier. It distinguishes `readonly ref` from `in` or `[In] ref`. | | ||
| | <xref:System.Runtime.CompilerServices.IsUnmanagedAttribute?displayProperty=fullName> | This attribute specifies the `unmanaged` constraint on a type parameter. | | ||
| | <xref:System.Runtime.CompilerServices.NullableAttribute?displayProperty=fullName>, <xref:System.Runtime.CompilerServices.NullableContextAttribute?displayProperty=fullName>, <xref:System.Runtime.CompilerServices.NullablePublicOnlyAttribute?displayProperty=fullName> | These attributes encode nullable annotations in your source code. | | ||
| | <xref:System.ParamArrayAttribute?displayProperty=fullName> | This attribute encodes the `params` modifier on array parameters. | | ||
| | <xref:System.Runtime.CompilerServices.ParamCollectionAttribute?displayProperty=fullName> | This attribute encodes the `params` modifier on non-array parameters. | | ||
| | <xref:System.Runtime.CompilerServices.RefSafetyRulesAttribute?displayProperty=fullName> | This attribute specifies the C# version that is required in order to understand ref safety annotations in the assembly. Ref safety rules evolve as C# gets new features. | | ||
| | <xref:System.Runtime.CompilerServices.RequiredMemberAttribute?displayProperty=fullName> | This attribute indicates that the `required` modifier was placed on a member declaration. It's the encoding of the [required members](../keywords/required.md) language feature. | | ||
| | <xref:System.Runtime.CompilerServices.TupleElementNamesAttribute?displayProperty=fullName> | This attribute encodes tuple element names used in signatures. | | ||
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| In addition, the compiler can generate a declaration for other attributes used internally. The compiler generates these in the <xref:System.Runtime.CompilerServices> namespace for its own use. Some aren't in the .NET Runtime libraries. Instead, the compiler synthesizes a definition for an `internal` type declaration in any assembly where the attribute is needed. | ||
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This one could have a note parallel to the note added for
InAttribute, saying "Use theoutmodifier."