debugging result

Chapter09/.gitignore

@@ -0,0 +1 @@
+data.txt

Chapter09/Cargo.toml

@@ -67,3 +67,7 @@ path = "performance_exponential.rs"
 [[bin]]
 name = "performance_reference"
 path = "performance_reference.rs"
+
+[[bin]]
+name = "debugging_result"
+path = "debugging_result.rs"

Chapter09/debugging_result.rs

@@ -0,0 +1,50 @@
+fn expect_1or2or_other(n: u64) -> Option<u64> {
+   match n {
+     1|2 => Some(n),
+     _ => None
+   }
+}
+
+fn expect_1or2or_error(n: u64) -> Result<u64,()> {
+   match n {
+     1|2 => Ok(n),
+     _ => Err(())
+   }
+}
+
+fn mixed_1or2() -> Result<(),()> {
+   expect_1or2or_other(1);
+   expect_1or2or_other(2);
+   expect_1or2or_other(3);
+
+   expect_1or2or_error(1)?;
+   expect_1or2or_error(2)?;
+   expect_1or2or_error(3).unwrap_or(222);
+
+   Ok(())
+}
+
+use std::fs::File;
+use std::io::prelude::*;
+use std::io;
+
+fn lots_of_io() -> io::Result<()> {
+   {
+      let mut file = File::create("data.txt")?;
+      file.write_all(b"data\ndata\ndata")?;
+   }
+   {
+      let mut file = File::open("data.txt")?;
+      let mut data = String::new();
+      file.read_to_string(&mut data)?;
+      println!("{}", data);
+   }
+
+   Ok(())
+}
+
+fn main() {
+   mixed_1or2().expect("mixed 1 or 2 is OK.");
+
+   lots_of_io().expect("lots of io is OK.");
+}