From acb122c0fcb3757aef2dc31a4757c1215b2917cf Mon Sep 17 00:00:00 2001
From: Stefan Kreutz <mail@skreutz.com>
Date: Sun, 25 Dec 2022 19:41:02 +0100
Subject: Implement size_hint, FusedIterator, ExactIterator

---
 CHANGELOG.md | 12 +++++++++---
 src/lib.rs   | 22 +++++++++++++++++++++-
 2 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4dd07b2..548607b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,17 +10,23 @@ The format is based on [Keep A Changelog][] and this project adheres to
 
 ## Unreleased
 
+### Changed
+
+- Implemented `Iterator::size_hint` for `ParallelMap`
+- Implemented `FusedIterator` for `ParallelMap`
+- Implemented `ExactSizeIterator` for `ParallelMap`
+
 ## [0.1.1] - 2022-12-21
 
 Improved documentation and tests.
 
 ### Added
 
-- Added recursive SHA256 example application.
+- Added recursive SHA256 example application
 
 ### Changed
 
-- `ParallelIterator` and `ParallelMap` must be used.
+- `ParallelIterator` and `ParallelMap` must be used
 
 ## [0.1.0] - 2022-12-18
 
@@ -28,4 +34,4 @@ Released the first version.
 
 ### Added
 
-- Added initial implementation.
+- Added initial implementation
diff --git a/src/lib.rs b/src/lib.rs
index 9c030d0..2d34b1c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -44,7 +44,7 @@
 #![forbid(unsafe_code)]
 #![warn(missing_docs)]
 
-use std::{collections::HashMap, num::NonZeroUsize};
+use std::{collections::HashMap, iter::FusedIterator, num::NonZeroUsize};
 
 use crossbeam_channel::{Receiver, Select, Sender, TryRecvError};
 
@@ -295,6 +295,26 @@ where
             }
         }
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (lower, upper) = self.iter.size_hint();
+        let inflight = self.inflight();
+        (
+            lower.saturating_add(inflight),
+            upper.and_then(|i| i.checked_add(inflight)),
+        )
+    }
+}
+
+impl<I, B> FusedIterator for ParallelMap<I, B> where I: FusedIterator {}
+
+impl<I, B> ExactSizeIterator for ParallelMap<I, B>
+where
+    I: ExactSizeIterator,
+{
+    fn len(&self) -> usize {
+        self.iter.len() + self.inflight()
+    }
 }
 
 /// Calls a given closure when the thread unwinds due to a panic.
-- 
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