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Editorial changes. #120
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Editorial changes. #120
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### Terminology | ||
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Reference types are types of the form `&T`, `&mut T` or `&dyn T`. | ||
Reference types are types of the form `&T`, `&mut T`. | ||
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Raw pointer types are types of the form `*const T` or `*mut T`. | ||
We write `*T` when the mutability attribute is unimportant. | ||
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### Representation | ||
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The alignment of `&T`, `&mut T`, `*const T` and `*mut T` are the same, | ||
and are at least the word size. | ||
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* If `T` is a trait, then the alignment of `&dyn T` is the word size. | ||
* If `T` is a sized type then the alignment of `&T` is the word size. | ||
* The alignment of `&dyn Trait` is the word size. | ||
* The alignment of `&[T]` is the word size. | ||
* The alignment of `&str` is the word size. | ||
* Alignment in other cases may be more than the word size (e.g., for other dynamically sized types). | ||
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The sizes of `&T`, `&mut T`, `*const T` and `*mut T` are the same, | ||
and are at least one word. | ||
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* If `T` is a trait, then the size of `&dyn T` is two words. | ||
* If `T` is a sized type then the size of `&T` is one word. | ||
* The size of `&dyn Trait` is two words. | ||
* The size of `&[T]` is two words. | ||
* The size of `&str` is two words. | ||
* Size in other cases may be more than one word (e.g., for other dynamically sized types). | ||
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### Notes | ||
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The layouts of `&T`, `&mut T` and `*T` are the same. | ||
The layouts of `&T`, `&mut T`, `*const T` and `*mut T` are the same. | ||
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If `T` is sized, references and pointers to `T` have a size and alignment of one | ||
word and have therefore the same layout as C pointers. | ||
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> or, in the case of `&mut T`, aliasing. | ||
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We do not make any guarantees about the layout of | ||
multi-trait objects `&(dyn T + U)` or references to other dynamically sized types, | ||
multi-trait objects `&(dyn Tr + Ur)` or references to other dynamically sized types, | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Maybe use There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Changed to Trait1 and Trait2. |
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other than that they are at least word-aligned, and have size at least one word. | ||
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The layout of `&dyn T` when `T` is a trait is the same as that of: | ||
```rust,ignore | ||
The layout of `&dyn Trait` when `Trait` is a trait is the same as that of: | ||
```rust | ||
#[repr(C)] | ||
struct DynObject { | ||
data: *u8, | ||
vtable: *u8, | ||
data: *const u8, | ||
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vtable: *const u8, | ||
} | ||
``` | ||
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The layout of `&[T]` is the same as that of: | ||
```rust,ignore | ||
```rust | ||
#[repr(C)] | ||
struct Slice<T> { | ||
ptr: *T, | ||
ptr: *const T, | ||
len: usize, | ||
} | ||
``` | ||
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