26 lines
2.1 KiB
Markdown
26 lines
2.1 KiB
Markdown
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# Aliasing allocators
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An **alias** is a collection which doesn't have its own allocation but instead shares the allocation of another collection, in whole or in part. For example, you can create an `UnsafeList` that doesn't allocate its own memory but instead uses a `NativeList`'s allocation. Writing to this shared memory via the `UnsafeList` affects the content of the `NativeList`, and vice versa.
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You don't need to dispose aliases, and calling `Dispose` on an alias does nothing. Once an original is disposed, you can no longer use the aliases of the original:
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[!code-cs[allocation_aliasing](../DocCodeSamples.Tests/CollectionsAllocationExamples.cs#allocation_aliasing)]
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Aliasing is useful for the following situations:
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* Getting a collection's data in the form of another collection type without copying the data. For example, you can create an `UnsafeList` that aliases a `NativeArray`.
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* Getting a subrange of a collection's data without copying the data. For example, you can create an UnsafeList that aliases a subrange of another list or array.
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* [Array reinterpretation](#array-reinterpretation).
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An `Unsafe-` collection can alias a `Native-` collection even though such cases undermine the safety checks. For example, if an `UnsafeList` aliases a `NativeList`, it's not safe to schedule a job that accesses one while also another job is scheduled that accesses the other, but the safety checks don't catch these cases.
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## Array reinterpretation
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A **reinterpretation** of an array is an alias of the array that reads and writes the content as a different element type. For example, a `NativeArray<int>` which reinterprets a `NativeArray<ushort>` shares the same bytes, but it reads and writes the bytes as an int instead of a ushort. This is because each int is 4 bytes while each ushort is 2 bytes. Each int corresponds to two ushorts, and the reinterpretation has half the length of the original.
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[!code-cs[allocation_reinterpretation](../DocCodeSamples.Tests/CollectionsAllocationExamples.cs#allocation_reinterpretation)]
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## Further information
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* [Define a custom allocator](allocator-custom-define.md)
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* [Rewindable allocators](allocator-rewindable.md)
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