| # Casts | |
| Casts are a superset of coercions: every coercion can be explicitly invoked via a cast. | |
| However some conversions require a cast. | |
| While coercions are pervasive and largely harmless, these "true casts" are rare and potentially dangerous. | |
| As such, casts must be explicitly invoked using the `as` keyword: `expr as Type`. | |
| You can find an exhaustive list of [all the true casts][cast list] and [casting semantics][semantics list] on the reference. | |
| ## Safety of casting | |
| True casts generally revolve around raw pointers and the primitive numeric types. | |
| Even though they're dangerous, these casts are infallible at runtime. | |
| If a cast triggers some subtle corner case no indication will be given that this occurred. | |
| The cast will simply succeed. | |
| That said, casts must be valid at the type level, or else they will be prevented statically. | |
| For instance, `7u8 as bool` will not compile. | |
| That said, casts aren't `unsafe` because they generally can't violate memory safety *on their own*. | |
| For instance, converting an integer to a raw pointer can very easily lead to terrible things. | |
| However the act of creating the pointer itself is safe, because actually using a raw pointer is already marked as `unsafe`. | |
| ## Some notes about casting | |
| ### Lengths when casting raw slices | |
| Note that lengths are not adjusted when casting raw slices; `*const [u16] as *const [u8]` creates a slice that only includes half of the original memory. | |
| ### Transitivity | |
| Casting is not transitive, that is, even if `e as U1 as U2` is a valid expression, `e as U2` is not necessarily so. | |
| [cast list]: ../reference/expressions/operator-expr.html#type-cast-expressions | |
| [semantics list]: ../reference/expressions/operator-expr.html#semantics |