| Adds a signed offset to a pointer. | |
| `count` is in units of T; e.g., a `count` of 3 represents a pointer | |
| offset of `3 * size_of::<T>()` bytes. | |
| # Safety | |
| If any of the following conditions are violated, the result is Undefined Behavior: | |
| * The offset in bytes, `count * size_of::<T>()`, computed on mathematical integers (without | |
| "wrapping around"), must fit in an `isize`. | |
| * If the computed offset is non-zero, then `self` must be [derived from][crate::ptr#provenance] a pointer to some | |
| [allocation], and the entire memory range between `self` and the result must be in | |
| bounds of that allocation. In particular, this range must not "wrap around" the edge | |
| of the address space. Note that "range" here refers to a half-open range as usual in Rust, | |
| i.e., `self..result` for non-negative offsets and `result..self` for negative offsets. | |
| Allocations can never be larger than `isize::MAX` bytes, so if the computed offset | |
| stays in bounds of the allocation, it is guaranteed to satisfy the first requirement. | |
| This implies, for instance, that `vec.as_ptr().add(vec.len())` (for `vec: Vec<T>`) is always | |
| safe. | |
| Consider using [`wrapping_offset`] instead if these constraints are | |
| difficult to satisfy. The only advantage of this method is that it | |
| enables more aggressive compiler optimizations. | |
| [`wrapping_offset`]: #method.wrapping_offset | |
| [allocation]: crate::ptr#allocation |