std: Add Option.{and,and_then,or,or_else}

Author: erickt

src/libextra/num/bigint.rs

@@ -635,7 +635,7 @@ impl BigUint {
 
     // Converts this BigUint into an int, unless it would overflow.
     pub fn to_int_opt(&self) -> Option<int> {
-        self.to_uint_opt().chain(|n| {
+        self.to_uint_opt().and_then(|n| {
             // If top bit of uint is set, it's too large to convert to
             // int.
             if (n >> (2*BigDigit::bits - 1) != 0) {
@@ -1221,7 +1221,7 @@ impl BigInt {
         match self.sign {
             Plus  => self.data.to_int_opt(),
             Zero  => Some(0),
-            Minus => self.data.to_uint_opt().chain(|n| {
+            Minus => self.data.to_uint_opt().and_then(|n| {
                 let m: uint = 1 << (2*BigDigit::bits-1);
                 if (n > m) {
                     None

src/libstd/option.rs

@@ -127,22 +127,51 @@ impl<T> Option<T> {
     #[inline]
     pub fn is_some(&self) -> bool { !self.is_none() }
 
-    /// Update an optional value by optionally running its content through a
-    /// function that returns an option.
+    /// Returns `None` if the option is `None`, otherwise returns `optb`.
     #[inline]
-    pub fn chain<U>(self, f: &fn(t: T) -> Option<U>) -> Option<U> {
+    pub fn and(self, optb: Option<T>) -> Option<T> {
         match self {
-            Some(t) => f(t),
-            None => None
+            Some(_) => optb,
+            None => None,
+        }
+    }
+
+    /// Returns `None` if the option is `None`, otherwise calls and returns the
+    /// value of `f`.
+    #[inline]
+    pub fn and_then(self, f: &fn() -> Option<T>) -> Option<T> {
+        match self {
+            Some(_) => f(),
+            None => None,
         }
     }
 
-    /// Returns the leftmost Some() value, or None if both are None.
+    /// Returns the option if it contains a value, otherwise returns `optb`.
     #[inline]
     pub fn or(self, optb: Option<T>) -> Option<T> {
         match self {
-            Some(opta) => Some(opta),
-            _ => optb
+            Some(_) => self,
+            None => optb
+        }
+    }
+
+    /// Returns the option if it contains a value, otherwise calls and returns the
+    /// value of `f`.
+    #[inline]
+    pub fn or_else(self, f: &fn() -> Option<T>) -> Option<T> {
+        match self {
+            Some(_) => self,
+            None => f(),
+        }
+    }
+
+    /// Update an optional value by optionally running its content through a
+    /// function that returns an option.
+    #[inline]
+    pub fn chain<U>(self, f: &fn(T) -> Option<U>) -> Option<U> {
+        match self {
+            Some(t) => f(t),
+            None => None
         }
     }
 
@@ -509,6 +538,50 @@ mod tests {
         let _y3 = y.take_unwrap();
     }
 
+    #[test]
+    fn test_and() {
+        let x: Option<int> = Some(1);
+        assert_eq!(x.and(Some(2)), Some(2));
+        assert_eq!(x.and(None), None);
+
+        let x: Option<int> = None;
+        assert_eq!(x.and(Some(2)), None);
+        assert_eq!(x.and(None), None);
+    }
+
+    #[test]
+    fn test_and_then() {
+        let x: Option<int> = Some(1);
+        assert_eq!(x.and_then(|| Some(2)), Some(2));
+        assert_eq!(x.and_then(|| None), None);
+
+        let x: Option<int> = None;
+        assert_eq!(x.and_then(|| Some(2)), None);
+        assert_eq!(x.and_then(|| None), None);
+    }
+
+    #[test]
+    fn test_or() {
+        let x: Option<int> = Some(1);
+        assert_eq!(x.or(Some(2)), Some(1));
+        assert_eq!(x.or(None), Some(1));
+
+        let x: Option<int> = None;
+        assert_eq!(x.or(Some(2)), Some(2));
+        assert_eq!(x.or(None), None);
+    }
+
+    #[test]
+    fn test_or_else() {
+        let x: Option<int> = Some(1);
+        assert_eq!(x.or_else(|| Some(2)), Some(1));
+        assert_eq!(x.or_else(|| None), Some(1));
+
+        let x: Option<int> = None;
+        assert_eq!(x.or_else(|| Some(2)), Some(2));
+        assert_eq!(x.or_else(|| None), None);
+    }
+
     #[test]
     fn test_option_while_some() {
         let mut i = 0;