Static mut
static mut is a Rust declaration for mutable statically allocated storage with a program-wide lifetime, whose access requires unsafe handling.
Rust in Action: Systems programming concepts and techniques
static mut declares a mutable Rust static variable with a program-wide lifetime and mutable access requiring unsafe handling.
- How it is used
- Deploys mutable global state for flags, error propagation, and communication with operating-system mechanisms such as signal handlers.
- How deep it goes
- Explains declaration and unsafe reads and writes through complete toy programs, but stops short of detailed concurrency guarantees.
- Examples
- Uses shutdown flags, random Boolean updates, global error codes, file operations, and panic output as concrete demonstrations.
- What you can do after
- Apply mutable statics in small Rust programs that use global flags or error state, while identifying why unsafe access demands caution.
Read how Rust in Action: Systems programming concepts and techniques explains static mut →
Learn Rust in a Month of Lunches
A static mut is a Rust static value that can be directly modified, but accessing it requires unsafe code because unsynchronized access can violate aliasing rules or cause data races.
- How it is used
- Introduces mutable statics as an entry point to unsafe Rust and contrasts them with safer ways to modify shared state.
- How deep it goes
- Demonstrates declaration, compiler rejection, unsafe access, and nondeterministic threaded results, but does not develop a safe replacement.
- Examples
- Uses NUMBER, a ten-thread increment test, and a thousand-thread stress test with inconsistent totals.
- What you can do after
- Diagnose why mutable-static access requires unsafe blocks and why unsynchronized increments can produce undefined behavior.
Read how Learn Rust in a Month of Lunches explains static mut →
Related concepts
- unsafe blockuses · An unsafe block is a Rust code region that permits operations whose safety requirements the compiler cannot verify and whose correctness requires programmer responsibility.
- unsafe Rustuses · Unsafe Rust is Rust code that permits operations whose safety conditions the compiler cannot fully verify and that therefore require the programmer to uphold the relevant invariants.
- static fieldkind of · A named variable whose storage is associated with a class or has static duration, rather than being allocated separately for each object instance or function call.
- global variablekind of · A global variable is a variable whose binding is accessible from broad program or module scope according to the language’s name-resolution rules.
- const qualifiercontrasts with · A language feature that marks a value, binding, or access path as constant, restricting reassignment or modification according to the language’s rules.
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