Merge pull request #51 from yuk1ty/lib-MultiWriter

feat: lib::io::MultiWriter を追加

Author: yuk1ty

lib/src/io.rs

@@ -0,0 +1,3 @@
+mod multi_writer;
+
+pub use multi_writer::MultiWriter;

lib/src/io/multi_writer.rs

@@ -0,0 +1,52 @@
+use std::io::{self, Write};
+
+/// Takes 0, 1, or more `std::io::Write`s and writes to them at a time.
+/// `MultiWriter` implements `std::io::Write` trait.
+///
+/// Inspired by Go's MultiWriter.
+///
+/// # Examples
+///
+/// ```
+/// use lib::io::MultiWriter;
+/// use std::{fs::File, io::{self, Write}};
+///
+/// fn main() -> io::Result<()> {
+///     let stdout = io::stdout();
+///     let f = File::create("a.txt")?;
+///
+///     let mut mw = MultiWriter::new(vec![Box::new(stdout), Box::new(f)]);
+///
+///     mw.write("xxx".as_bytes())?;
+///     mw.flush()?;
+///
+///     Ok(())
+/// }
+/// ```
+pub struct MultiWriter(Vec<Box<dyn Write>>);
+
+impl MultiWriter {
+    /// Constructor.
+    pub fn new(writers: Vec<Box<dyn Write>>) -> Self {
+        Self(writers)
+    }
+}
+
+impl Write for MultiWriter {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        for w in &mut self.0 {
+            // Using `Write::write` is more straightforward but
+            // it sometimes (especially when buf is large) writes only part of buf.
+            // To align bytes written for all writers (self.0), here uses `Write::write_all`.
+            w.write_all(buf)?;
+        }
+        Ok(buf.len())
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        for w in &mut self.0 {
+            w.flush()?;
+        }
+        Ok(())
+    }
+}

lib/src/lib.rs

@@ -1 +1 @@
-// 共通ライブラリ
+pub mod io;