Behavior not considered unsafe - The Rust Reference

## Behavior not considered `unsafe`

The Rust compiler does not consider the following behaviors unsafe, though a programmer may (should) find them undesirable, unexpected, or erroneous.

##### Deadlocks

##### Leaks of memory and other resources

##### Exiting without calling destructors

##### Exposing randomized base addresses through pointer leaks

##### Integer overflow

If a program contains arithmetic overflow, the programmer has made an error. In the following discussion, we maintain a distinction between arithmetic overflow and wrapping arithmetic. The first is erroneous, while the second is intentional.

When the programmer has enabled `debug_assert!` assertions (for example, by enabling a non-optimized build), implementations must insert dynamic checks that `panic` on overflow. Other kinds of builds may result in `panics` or silently wrapped values on overflow, at the implementation's discretion.

In the case of implicitly-wrapped overflow, implementations must provide well-defined (even if still considered erroneous) results by using two's complement overflow conventions.

The integral types provide inherent methods to allow programmers explicitly to perform wrapping arithmetic. For example, `i32::wrapping_add` provides two's complement, wrapping addition.

The standard library also provides a `Wrapping<T>` newtype which ensures all standard arithmetic operations for `T` have wrapping semantics.

See RFC 560 for error conditions, rationale, and more details about integer overflow.