为什么Rust枚举这么酷？

enum Colour {    Red,    Green,    Blue}

var colour1 = Colour.Red;var colour2 = Colour.Green;
//Compare colour1 and colour2 and do something if equalif (colour1 == colour2) {    //do something}

var colourInt = (int)colour1;

enum Option<T> {    None,    Some(T),}

class Nullable<T> {    public bool hasValue;    public T value;}

var mightBeNull = new Nullable<string>();if (mightBeNull.hasValue) {    //do something with mightBeNull.value}

var mightBeNull = new Nullable<string>();//no compiler error but still a NullReferenceExceptionvar length = mightBeNull.value.Length;

let might_be_null: Option<String> = Option::None;//error[E0609]: no field `value` on type `Option<String>`let some_other_var = might_be_null.value;

let might_be_null: Option<String> = //get an Option<String> from somewhereif let Some(value) = might_be_null {    //do something with value}

enum Result<T, E> {    Ok(T),    Err(E),}

double atof(const char* str);

fn atof(str: &str) -> Result<f64, u8> {    //...}

match atof("123.56") {    Ok(val) => { println!("Parsed value is: {}", val)}    Err(e) => { println!("Error is {}", e)}}

pub enum Value {    /// Represents a YAML null value.    Null,    /// Represents a YAML boolean.    Bool(bool),    /// Represents a YAML numerical value, whether integer or floating point.    Number(Number),    /// Represents a YAML string.    String(String),    /// Represents a YAML sequence in which the elements are    /// `serde_yaml::Value`.    Sequence(Sequence),    /// Represents a YAML mapping in which the keys and values are both    /// `serde_yaml::Value`.    Mapping(Mapping),}