pure

Declares that a function has no effects: pure fn name(…).

The compiler checks the promise: a call that reads or writes files, uses the network, the environment, threads or shared mutable state is error E0413. Panicking and building new objects are allowed. Contextual: only a keyword directly before fn.

pure fn area(int w, int h) -> int {
    return w * h;
}

See also#

• fn: Declares a function, a method, or (written in an expression) an anonymous function.
• let: Declares a mutable local variable.
• const: Declares a binding that cannot be reassigned: a local, a module constant, or a class field that is set only by new.
• static: Declares a module-level or class-level slot shared by the whole program, or a method without self.
• readonly: A read-only view of a value: nothing reachable through it can be changed.
• if: Runs a block when a bool condition is true.
• else: Introduces the branch of an if that runs when its condition is false (or its pattern does not match).
• while: Repeats a block while a bool condition is true.