diff --git a/src/expressions/operator-expr.md b/src/expressions/operator-expr.md index 55b7bbcb4..55dcbcb6a 100644 --- a/src/expressions/operator-expr.md +++ b/src/expressions/operator-expr.md @@ -454,35 +454,35 @@ Any cast that does not fit either a coercion rule or an entry in the table is a Here `*T` means either `*const T` or `*mut T`. `m` stands for optional `mut` in reference types and `mut` or `const` in pointer types. -| Type of `e` | `U` | Cast performed by `e as U` | -|-----------------------|-----------------------|----------------------------------| -| Integer or Float type | Integer or Float type | Numeric cast | -| Enumeration | Integer type | Enum cast | -| `bool` or `char` | Integer type | Primitive to integer cast | -| `u8` | `char` | `u8` to `char` cast | -| `*T` | `*V` where `V: Sized` \* | Pointer to pointer cast | -| `*T` where `T: Sized` | Integer type | Pointer to address cast | -| Integer type | `*V` where `V: Sized` | Address to pointer cast | -| `&m₁ T` | `*m₂ T` \*\* | Reference to pointer cast | -| `&m₁ [T; n]` | `*m₂ T` \*\* | Array to pointer cast | -| [Function item] | [Function pointer] | Function item to function pointer cast | -| [Function item] | `*V` where `V: Sized` | Function item to pointer cast | -| [Function item] | Integer | Function item to address cast | -| [Function pointer] | `*V` where `V: Sized` | Function pointer to pointer cast | -| [Function pointer] | Integer | Function pointer to address cast | -| Closure \*\*\* | Function pointer | Closure to function pointer cast | - -\* or `T` and `V` are unsized types with compatible metadata: - -* Both slice metadata (`*[u16]` -> `*[u8]`, `*str` -> `*(u8, [u32])`). -* Both the same trait object metadata, modulo dropping auto traits (`*dyn Debug` -> `*(u16, dyn Debug)`, `*dyn Debug + Send` -> `*dyn Debug`). - * **Note**: Adding auto traits is only allowed if the principal trait has the auto trait as a super trait (given `trait T: Send {}`, `*dyn T` -> `*dyn T + Send` is valid, but `*dyn Debug` -> `*dyn Debug + Send` is not). - * **Note**: Generics (including lifetimes) must match (`*dyn T<'a, A>` -> `*dyn T<'b, B>` requires `'a = 'b` and `A = B`). - -\*\* only when `m₁` is `mut` or `m₂` is `const`. Casting `mut` reference to +| Type of `e` | `U` | Cast performed by `e as U` | +|-----------------------|-----------------------|-------------------------------------------------------| +| Integer or Float type | Integer or Float type | [Numeric cast][expr.as.numeric] | +| Enumeration | Integer type | [Enum cast][expr.as.enum] | +| `bool` or `char` | Integer type | [Primitive to integer cast][expr.as.bool-char-as-int] | +| `u8` | `char` | [`u8` to `char` cast][expr.as.u8-as-char] | +| `*T` | `*V` [^meta-compat] | [Pointer to pointer cast][expr.as.pointer] | +| `*T` where `T: Sized` | Integer type | [Pointer to address cast][expr.as.pointer-as-int] | +| Integer type | `*V` where `V: Sized` | [Address to pointer cast][expr.as.int-as-pointer] | +| `&m₁ [T; n]` | `*m₂ T` [^lessmut] | Array to pointer cast | +| `*m₁ [T; n]` | `*m₂ T` [^lessmut] | Array to pointer cast | +| [Function item] | [Function pointer] | Function item to function pointer cast | +| [Function item] | `*V` where `V: Sized` | Function item to pointer cast | +| [Function item] | Integer | Function item to address cast | +| [Function pointer] | `*V` where `V: Sized` | Function pointer to pointer cast | +| [Function pointer] | Integer | Function pointer to address cast | +| Closure [^no-capture] | Function pointer | Closure to function pointer cast | + +[^meta-compat]: where `T` and `V` have compatible metadata: + * `V: Sized`, or + * Both slice metadata (`*[u16]` -> `*[u8]`, `*str` -> `*(u8, [u32])`), or + * Both the same trait object metadata, modulo dropping auto traits (`*dyn Debug` -> `*(u16, dyn Debug)`, `*dyn Debug + Send` -> `*dyn Debug`) + * **Note**: *adding* auto traits is only allowed if the principal trait has the auto trait as a super trait (given `trait T: Send {}`, `*dyn T` -> `*dyn T + Send` is valid, but `*dyn Debug` -> `*dyn Debug + Send` is not) + * **Note**: Generics (including lifetimes) must match (`*dyn T<'a, A>` -> `*dyn T<'b, B>` requires `'a = 'b` and `A = B`) + +[^lessmut]: only when `m₁` is `mut` or `m₂` is `const`. Casting `mut` reference/pointer to `const` pointer is allowed. -\*\*\* only for closures that do not capture (close over) any local variables +[^no-capture]: only for closures that do not capture (close over) any local variables can be casted to function pointers. ### Semantics