Add a for_each convenience function

Freaky · Jan 5, 2019 · fa8cb22 · fa8cb22
1 parent 38f58d0
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diff --git a/README.md b/README.md
@@ -5,7 +5,7 @@
 `LineReader` is a byte-delimiter-focused buffered reader for Rust, meant as a
 faster, less error-prone alternative to `BufRead::read_until`.
 
-It provides two main functions:
+It provides three main functions:
 
 
 ### `next_line()`
@@ -28,6 +28,13 @@ Behaves identically to `next_line()`, except it returns a slice of *all* the
 complete lines in the buffer.
 
 
+### `for_each()`
+
+Calls a closure on each line of the input, while the closure returns true and
+no IO errors are detected.  Such errors terminate iteration and are returned
+from the function.
+
+
 ## Example
 
 ```rust

diff --git a/src/lib.rs b/src/lib.rs
@@ -120,6 +120,29 @@ impl<R: io::Read> LineReader<R> {
         }
     }
 
+    /// Run the given closure for each line while the closure returns true.
+    ///
+    /// ```no_run
+    /// # use linereader::LineReader;
+    /// # use std::fs::File;
+    /// # use std::io;
+    /// # fn solve(x: &[u8]) { }
+    /// # fn x() -> io::Result<()> {
+    /// # let mut reader = LineReader::new(File::open("myfile.txt")?);
+    /// reader.for_each(|line| { if line.len() == 42 { solve(line); true } else { false } })?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn for_each<F: FnMut(&[u8]) -> bool>(&mut self, mut f: F) -> io::Result<()> {
+        while let Some(line) = self.next_line() {
+            if !f(line?) {
+                break;
+            }
+        }
+
+        Ok(())
+    }
+
     /// Get the next line from the reader, an IO error, or `None` on EOF.  The delimiter
     /// is included in any returned slice, unless the file ends without one or a line was
     /// truncated to the buffer size due to length.
@@ -314,6 +337,20 @@ mod tests {
         assert_eq!(b"7hhhhhh7", reader.next_batch().unwrap().unwrap());
     }
 
+    #[test]
+    fn test_for_each() {
+        let buf: &[u8] = b"f\nba\nbaz\n";
+        let mut reader = LineReader::new(buf);
+
+        let mut len = 2;
+        reader.for_each(|l| { assert_eq!(len, l.len()); len += 1; true }).unwrap();
+
+        let buf: &[u8] = b"f\nba\nbaz\n";
+        let mut reader = LineReader::new(buf);
+
+        reader.for_each(|l| { assert_eq!(l.len(), 2); false }).unwrap();
+    }
+
     extern crate rand;
     use std::io::BufRead;
     use std::io::{Cursor, Read};