Exclamation mark in Rust !

There are a number of places where we can see exclamation marks ! in Rust.

Never type

As the designated return type of a function:

fn foo() -> ! {
    ...
}

Diverging Functions - functions that never return

Macros

At the end of "function" names:

println!("Hello World");

Functions that end with an exclamation mark !

Boolean not

In boolean expressions:

if ! var.is_empty() {
   ...
}

Boolean not !

Not equal !=

Comparing values for lack of equality:

if answer != 42 {
    ...
}