dedicated sink newtypes for fmt::Write and io::Write

src/sink.rs

@@ -12,45 +12,42 @@ pub trait StrSink {
     }
 }
 
-impl<W> StrSink for W
-where
-    W: fmt::Write,
-{
+pub trait FmtSink: StrSink {
+    fn sink_fmt<'a>(&mut self, args: Arguments<'a>) -> Result<(), <Self as StrSink>::Error>;
+}
+
+#[macro_export]
+macro_rules! sink_fmt {
+    ($dst:expr, $($arg:tt)*) => {
+        FmtSink::sink_fmt($dst, core::format_args!($($arg)*))
+    };
+}
+
+pub use sink_fmt;
+
+pub struct FmtWriteSink<W: fmt::Write>(pub W);
+
+impl<W: fmt::Write> StrSink for FmtWriteSink<W> {
     type Error = fmt::Error;
 
     #[inline]
     fn sink_str(&mut self, s: &str) -> Result<(), Self::Error> {
-        self.write_str(s)
+        self.0.write_str(s)
     }
 
     #[inline]
     fn sink_char(&mut self, c: char) -> Result<(), Self::Error> {
-        self.write_char(c)
+        self.0.write_char(c)
     }
 }
 
-pub trait FmtSink: StrSink {
-    fn sink_fmt<'a>(&mut self, args: Arguments<'a>) -> Result<(), <Self as StrSink>::Error>;
-}
-
-impl<W> FmtSink for W
-where
-    W: fmt::Write,
-{
+impl<W: fmt::Write> FmtSink for FmtWriteSink<W> {
+    #[inline]
     fn sink_fmt<'a>(&mut self, args: Arguments<'a>) -> Result<(), <Self as StrSink>::Error> {
-        self.write_fmt(args)
+        self.0.write_fmt(args)
     }
 }
 
-#[macro_export]
-macro_rules! sink_fmt {
-    ($dst:expr, $($arg:tt)*) => {
-        FmtSink::sink_fmt($dst, core::format_args!($($arg)*))
-    };
-}
-
-pub use sink_fmt;
-
 #[cfg(feature = "alloc")]
 pub use string_sink::SinkString;
 
@@ -138,3 +135,33 @@ mod string_sink {
         }
     }
 }
+
+#[cfg(feature = "std")]
+pub use io_sink::IoWriteSink;
+
+#[cfg(feature = "std")]
+mod io_sink {
+    use core::fmt::Arguments;
+    use std::io;
+
+    use super::{StrSink, FmtSink};
+    
+    #[repr(transparent)]
+    pub struct IoWriteSink<W: io::Write>(pub W);
+
+    impl<W: io::Write> StrSink for IoWriteSink<W> {
+        type Error = io::Error;
+
+        #[inline]
+        fn sink_str(&mut self, s: &str) -> Result<(), Self::Error> {
+            self.0.write_all(s.as_bytes())
+        }
+    }
+
+    impl<W: io::Write> FmtSink for IoWriteSink<W> {
+        #[inline]
+        fn sink_fmt<'a>(&mut self, args: Arguments<'a>) -> Result<(), <Self as StrSink>::Error> {
+            self.0.write_fmt(args)
+        }
+    }
+}