Minimize the cost of write_fmt without arguments

tesuji · tesuji · commit 23fdb5520757 · 2020-08-10T09:41:57.000Z
diff --git a/library/core/src/fmt/mod.rs b/library/core/src/fmt/mod.rs
@@ -190,7 +190,10 @@ pub trait Write {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     fn write_fmt(mut self: &mut Self, args: Arguments<'_>) -> Result {
-        write(&mut self, args)
+        match args.as_str() {
+            Some(s) => self.write_str(s),
+            None => write(&mut self, args),
+        }
     }
 }
 
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
@@ -1506,15 +1506,19 @@ pub trait Write {
             }
         }
 
-        let mut output = Adaptor { inner: self, error: Ok(()) };
-        match fmt::write(&mut output, fmt) {
-            Ok(()) => Ok(()),
-            Err(..) => {
-                // check if the error came from the underlying `Write` or not
-                if output.error.is_err() {
-                    output.error
-                } else {
-                    Err(Error::new(ErrorKind::Other, "formatter error"))
+        if let Some(s) = fmt.as_str() {
+            self.write_all(s.as_bytes())
+        } else {
+            let mut output = Adaptor { inner: self, error: Ok(()) };
+            match fmt::write(&mut output, fmt) {
+                Ok(()) => Ok(()),
+                Err(..) => {
+                    // check if the error came from the underlying `Write` or not
+                    if output.error.is_err() {
+                        output.error
+                    } else {
+                        Err(Error::new(ErrorKind::Other, "formatter error"))
+                    }
                 }
             }
         }
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
@@ -265,6 +265,7 @@
 #![feature(exhaustive_patterns)]
 #![feature(extend_one)]
 #![feature(external_doc)]
+#![feature(fmt_as_str)]
 #![feature(fn_traits)]
 #![feature(format_args_nl)]
 #![feature(future_readiness_fns)]

Original file line number	Diff line number	Diff line change
`@@ -190,7 +190,10 @@ pub trait Write {`
`190`	`190`	/// ```
`191`	`191`	`#[stable(feature = "rust1", since = "1.0.0")]`
`192`	`192`	`fn write_fmt(mut self: &mut Self, args: Arguments<'_>) -> Result {`
`193`		`- write(&mut self, args)`
	`193`	`+ match args.as_str() {`
	`194`	`+ Some(s) => self.write_str(s),`
	`195`	`+ None => write(&mut self, args),`
	`196`	`+ }`
`194`	`197`	`}`
`195`	`198`	`}`
`196`	`199`
Original file line number	Diff line number	Diff line change
`@@ -1506,15 +1506,19 @@ pub trait Write {`
`1506`	`1506`	`}`
`1507`	`1507`	`}`
`1508`	`1508`
`1509`		`- let mut output = Adaptor { inner: self, error: Ok(()) };`
`1510`		`- match fmt::write(&mut output, fmt) {`
`1511`		`- Ok(()) => Ok(()),`
`1512`		`- Err(..) => {`
`1513`		- // check if the error came from the underlying `Write` or not
`1514`		`- if output.error.is_err() {`
`1515`		`- output.error`
`1516`		`- } else {`
`1517`		`- Err(Error::new(ErrorKind::Other, "formatter error"))`
	`1509`	`+ if let Some(s) = fmt.as_str() {`
	`1510`	`+ self.write_all(s.as_bytes())`
	`1511`	`+ } else {`
	`1512`	`+ let mut output = Adaptor { inner: self, error: Ok(()) };`
	`1513`	`+ match fmt::write(&mut output, fmt) {`
	`1514`	`+ Ok(()) => Ok(()),`
	`1515`	`+ Err(..) => {`
	`1516`	+ // check if the error came from the underlying `Write` or not
	`1517`	`+ if output.error.is_err() {`
	`1518`	`+ output.error`
	`1519`	`+ } else {`
	`1520`	`+ Err(Error::new(ErrorKind::Other, "formatter error"))`
	`1521`	`+ }`
`1518`	`1522`	`}`
`1519`	`1523`	`}`
`1520`	`1524`	`}`