nomicon/uninitialized.md

% Working With Uninitialized Memory

All runtime-allocated memory in a Rust program begins its life as
*uninitialized*. In this state the value of the memory is an indeterminate pile
of bits that may or may not even reflect a valid state for the type that is
supposed to inhabit that location of memory. Attempting to interpret this memory
as a value of *any* type will cause Undefined Behaviour. Do Not Do This.

Rust provides mechanisms to work with uninitialized memory in checked (safe) and
unchecked (unsafe) ways.