Functions

Unlike in Java where methods are mainly used to add behaviour to types (and therefore are tied to those types), Rust supports stand-alone functions. Rust also supports methods (and associated functions) that are tied to types (structs and enums).

Consider the following example method in Java:

// A method to calculate the area of a rectangle
double areaOfRectangle(double length, double width) {
    return length * width;
}

This is how the equivalent function looks like in Rust:

// A function to calculate the area of a rectangle
fn area_of_rectangle(length: f64, width: f64) -> f64 {
	length * width // No semi-colon needed here. The expression is evaluated and the result returned
}

This would still work but it's not idiomatic Rust:

fn area_of_rectangle(length: f64, width: f64) -> f64 {
	return length * width; // using a return statement works, but it's not idiomatic Rust
}

Here are a few things to note:

• In Rust, functions are defined with fn.
• Rust uses snake_case for function names (and for variable names as well).
• Unlike in Java, types are declared second in Rust (length: f64).
• In Rust, -> signifies the return type of a function.
• In Rust, the idiomatic way to return from a function is to not terminate with semi-colon.