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Array initialization using non-Copy types requires feature gate

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Philipp Oppermann
2020-01-15 18:06:30 +01:00
parent 658212c1f5
commit 687c81eedb
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blog/content/second-edition/posts/11-allocator-designs/index.md
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@@ -925,9 +925,12 @@ impl FixedSizeBlockAllocator {
} }
``` ```
The `new` function just initializes the `list_heads` array with empty nodes and creates an [`empty`] linked list allocator as `fallback_allocator`. The unsafe `init` function only calls the [`init`] function of the `fallback_allocator` without doing any additional initialization of the `list_heads` array. The `new` function just initializes the `list_heads` array with empty nodes and creates an [`empty`] linked list allocator as `fallback_allocator`. Since array initializations using non-`Copy` types are still unstable, we need to add **`#![feature(const_in_array_repeat_expressions)]`** to the beginning of our `lib.rs`. The reason that `None` is not `Copy` in this case is that `ListNode` does not implement `Copy`. Thus, the `Option` wrapper and its `None` variant are not `Copy` either.
[`empty`]: https://docs.rs/linked_list_allocator/0.6.4/linked_list_allocator/struct.Heap.html#method.empty [`empty`]: https://docs.rs/linked_list_allocator/0.6.4/linked_list_allocator/struct.Heap.html#method.empty
The unsafe `init` function only calls the [`init`] function of the `fallback_allocator` without doing any additional initialization of the `list_heads` array. Instead, we will initialize the lists lazily on `alloc` and `dealloc` calls.
[`init`]: https://docs.rs/linked_list_allocator/0.6.4/linked_list_allocator/struct.Heap.html#method.init [`init`]: https://docs.rs/linked_list_allocator/0.6.4/linked_list_allocator/struct.Heap.html#method.init
For convenience, we also create a private `fallback_alloc` method that allocates using the `fallback_allocator`: For convenience, we also create a private `fallback_alloc` method that allocates using the `fallback_allocator`: