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