rust/src/libcore/option.rs
Marijn Haverbeke ffd50b9cdf Make the various from_str functions return options
So that they can be used with user input without causing task
failures.

Closes #1335
2012-02-22 13:18:15 +01:00

155 lines
3.0 KiB
Rust

/*
Module: option
Represents the presence or absence of a 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.
*/
/*
Tag: t
The option type
*/
enum t<T> {
/* Variant: none */
none,
/* Variant: some */
some(T),
}
/* Section: Operations */
/*
Function: get
Gets the value out of an option
Failure:
Fails if the value equals `none`.
*/
pure fn get<T: copy>(opt: t<T>) -> T {
alt opt { some(x) { ret x; } none { fail "option none"; } }
}
/*
*/
fn map<T, U: copy>(opt: t<T>, f: fn(T) -> U) -> t<U> {
alt opt { some(x) { some(f(x)) } none { none } }
}
/*
Function: chain
Update an optional value by optionally running its content through a function
that returns an option.
*/
fn chain<T, U>(opt: t<T>, f: fn(T) -> t<U>) -> t<U> {
alt opt { some(x) { f(x) } none { none } }
}
/*
Function: is_none
Returns true if the option equals none
*/
pure fn is_none<T>(opt: t<T>) -> bool {
alt opt { none { true } some(_) { false } }
}
/*
Function: is_some
Returns true if the option contains some value
*/
pure fn is_some<T>(opt: t<T>) -> bool { !is_none(opt) }
/*
Function: from_maybe
Returns the contained value or a default
*/
pure fn from_maybe<T: copy>(def: T, opt: t<T>) -> T {
alt opt { some(x) { x } none { def } }
}
/*
Function: maybe
Applies a function to the contained value or returns a default
*/
fn maybe<T, U: copy>(def: U, opt: t<T>, f: fn(T) -> U) -> U {
alt opt { none { def } some(t) { f(t) } }
}
// FIXME: Can be defined in terms of the above when/if we have const bind.
/*
Function: may
Performs an operation on the contained value or does nothing
*/
fn may<T>(opt: t<T>, f: fn(T)) {
alt opt { none {/* nothing */ } some(t) { f(t); } }
}
/*
Function: unwrap
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.
*/
fn unwrap<T>(-opt: t<T>) -> T unsafe {
let addr = alt opt {
some(x) { ptr::addr_of(x) }
none { fail "option none" }
};
let liberated_value = unsafe::reinterpret_cast(*addr);
unsafe::leak(opt);
ret liberated_value;
}
#[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() {
resource r(i: @mutable int) {
*i += 1;
}
let i = @mutable 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: