rust/src/libcore/option.rs

187 lines
4.7 KiB
Rust

/*!
* Operations on the ubiquitous `option` type.
*
* Type `option` represents an optional value.
*
* Every `option<T>` value can either be `some(T)` or `none`. Where in other
* languages you might use a nullable type, in Rust you would use an option
* type.
*/
/// The option type
enum option<T> {
none,
some(T),
}
pure fn get<T: copy>(opt: option<T>) -> T {
/*!
* Gets the value out of an option
*
* # Failure
*
* Fails if the value equals `none`
*/
alt opt { some(x) { ret x; } none { fail "option none"; } }
}
pure fn expect<T: copy>(opt: option<T>, reason: str) -> T {
#[doc = "
Gets the value out of an option, printing a specified message on failure
# Failure
Fails if the value equals `none`
"];
alt opt { some(x) { x } none { fail reason; } }
}
pure fn map<T, U: copy>(opt: option<T>, f: fn(T) -> U) -> option<U> {
//! Maps a `some` value from one type to another
alt opt { some(x) { some(f(x)) } none { none } }
}
pure fn chain<T, U>(opt: option<T>, f: fn(T) -> option<U>) -> option<U> {
/*!
* Update an optional value by optionally running its content through a
* function that returns an option.
*/
alt opt { some(x) { f(x) } none { none } }
}
pure fn is_none<T>(opt: option<T>) -> bool {
//! Returns true if the option equals `none`
alt opt { none { true } some(_) { false } }
}
pure fn is_some<T>(opt: option<T>) -> bool {
//! Returns true if the option contains some value
!is_none(opt)
}
pure fn get_default<T: copy>(opt: option<T>, def: T) -> T {
//! Returns the contained value or a default
alt opt { some(x) { x } none { def } }
}
pure fn map_default<T, U: copy>(opt: option<T>, def: U, f: fn(T) -> U) -> U {
//! Applies a function to the contained value or returns a default
alt opt { none { def } some(t) { f(t) } }
}
pure fn iter<T>(opt: option<T>, f: fn(T)) {
//! Performs an operation on the contained value or does nothing
alt opt { none { } some(t) { f(t); } }
}
pure fn unwrap<T>(-opt: option<T>) -> T {
/*!
* Moves a value out of an option type and returns it.
*
* Useful primarily for getting strings, vectors and unique pointers out
* of option types without copying them.
*/
unsafe {
let addr = alt opt {
some(x) { ptr::addr_of(x) }
none { fail "option none" }
};
let liberated_value = unsafe::reinterpret_cast(*addr);
unsafe::forget(opt);
ret liberated_value;
}
}
impl extensions<T> for option<T> {
/**
* Update an optional value by optionally running its content through a
* function that returns an option.
*/
fn chain<U>(f: fn(T) -> option<U>) -> option<U> { chain(self, f) }
/// Applies a function to the contained value or returns a default
fn map_default<U: copy>(def: U, f: fn(T) -> U) -> U
{ map_default(self, def, f) }
/// Performs an operation on the contained value or does nothing
fn iter(f: fn(T)) { iter(self, f) }
/// Returns true if the option equals `none`
fn is_none() -> bool { is_none(self) }
/// Returns true if the option contains some value
fn is_some() -> bool { is_some(self) }
/// Maps a `some` value from one type to another
fn map<U:copy>(f: fn(T) -> U) -> option<U> { map(self, f) }
}
impl extensions<T: copy> for option<T> {
/**
* Gets the value out of an option
*
* # Failure
*
* Fails if the value equals `none`
*/
fn get() -> T { get(self) }
fn get_default(def: T) -> T { get_default(self, def) }
/**
* Gets the value out of an option, printing a specified message on
* failure
*
* # Failure
*
* Fails if the value equals `none`
*/
pure fn expect(reason: str) -> T { expect(self, reason) }
}
#[test]
fn test_unwrap_ptr() {
let x = ~0;
let addr_x = ptr::addr_of(*x);
let opt = some(x);
let y = unwrap(opt);
let addr_y = ptr::addr_of(*y);
assert addr_x == addr_y;
}
#[test]
fn test_unwrap_str() {
let x = "test";
let addr_x = str::as_buf(x, |buf| ptr::addr_of(buf));
let opt = some(x);
let y = unwrap(opt);
let addr_y = str::as_buf(y, |buf| ptr::addr_of(buf));
assert addr_x == addr_y;
}
#[test]
fn test_unwrap_resource() {
class r {
let i: @mut int;
new(i: @mut int) { self.i = i; }
drop { *(self.i) += 1; }
}
let i = @mut 0;
{
let x = r(i);
let opt = some(x);
let _y = unwrap(opt);
}
assert *i == 1;
}
// Local Variables:
// mode: rust;
// fill-column: 78;
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// End: