Move from a helper function to a typeclass.

This introduces the `FoldResut` trait to move from `func(receiver, ...)`
style to `receiver.func(...)` style. Also add a means to pass the
default result explicitly.

1 files changed, 29 insertions, 7 deletions

diff --git a/libimagutil/src/iter.rs b/libimagutil/src/iter.rs
index 0f682bff..52d723bf 100644
--- a/libimagutil/src/iter.rs
+++ b/libimagutil/src/iter.rs
@@ -1,8 +1,30 @@
-/// Processes `iter` returning the last successful result or the first error.
-pub fn fold_ok<X, I, R, E, F>(iter: I, mut func: F) -> Result<R, E>
-    where I: Iterator<Item = X>,
-          R: Default,
-          F: FnMut(X) -> Result<R, E>
-{
-    iter.fold(Ok(R::default()), |acc, item| acc.and_then(|_| func(item)))
+/// Folds its contents to a result.
+pub trait FoldResult: Sized {
+    type Item;
+
+    /// Processes all contained items returning the last successful result or the first error.
+    /// If there are no items, returns `Ok(R::default())`.
+    fn fold_defresult<R, E, F>(self, func: F) -> Result<R, E>
+        where R: Default,
+              F: FnMut(Self::Item)
+        -> Result<R, E>
+    {
+        self.fold_result(R::default(), func)
+    }
+
+    /// Processes all contained items returning the last successful result or the first error.
+    /// If there are no items, returns `Ok(default)`.
+    fn fold_result<R, E, F>(self, default: R, mut func: F) -> Result<R, E>
+        where F: FnMut(Self::Item) -> Result<R, E>;
 }
+
+impl<X, I: Iterator<Item = X>> FoldResult for I {
+    type Item = X;
+
+    fn fold_result<R, E, F>(self, default: R, mut func: F) -> Result<R, E>
+        where F: FnMut(Self::Item) -> Result<R, E>
+    {
+        self.fold(Ok(default), |acc, item| acc.and_then(|_| func(item)))
+    }
+}
+