added result

Author: BartMassey

README.md

@@ -5,17 +5,18 @@ Various small examples from my Rust course. Previously a lot
 of these were on the playground, but I prefer to have them
 in a controlled repository now.
 
-* `datatypes`: examples of various datatype thingies
+* `datatypes/`: examples of various datatype thingies
 * `structs.rs`: struct and enum examples
 * `arrays.rs`: array and vector examples
 * `strings.rs`: string and str examples
 * `iterators.rs`: iterator examples
 * `closures.rs`: closure examples
 * `lifetimes.rs`: simple lifetime example
-* `rc`: examples with `RefCell` and `Rc`
-* `readline`: example of readline with error handling
-* `error`: example of creating a custom error
-* `modules`: example of modules
+* `rc/`: examples with `RefCell` and `Rc`
+* `readline/`: example of readline with error handling
+* `error/`: example of creating a custom error
+* `modules/`: example of modules
 * `point.rs`: example of "methods" and ownership
 * `units.rs`: example of newtype and deriving
 * `patmove.rs`: example of `ref` in patterns
+* `result/`: example of defining and using `Result`

result/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "result"
+version = "0.1.0"
+authors = ["Bart Massey <[email protected]>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+
+[[bin]]
+name = "result"
+path = "result.rs"
+
+[features]
+myerror = []
+default_features = []

result/result.rs

@@ -0,0 +1,51 @@
+use std::io::Read;
+
+#[cfg(feature = "ownerror")]
+mod my_result {
+    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    enum MyResult<T, E> {
+        Ok(T),
+        Err(E),
+    }
+
+    impl<T, E> MyResult<T, E> {
+        fn new(x: Result<T, E>) -> Self {
+            match x {
+                Ok(x) => MyResult::Ok(x),
+                Err(x) => MyResult::Err(x),
+            }
+        }
+
+        fn unwrap(self) -> T
+            where E: std::error::Error
+        {
+            match self {
+                MyResult::Ok(v) => v,
+                MyResult::Err(e) => panic!("unwrap failed: {}", e),
+            }
+        }
+    }
+}
+
+fn read_file_as_string<P>(filename: P) -> Result<(usize, String), Box<dyn std::error::Error>>
+    where P: AsRef<std::path::Path>
+{
+    let mut f = std::fs::File::open(filename.as_ref())?;
+    let mut bytes: Vec<u8> = Vec::with_capacity(1024);
+    let n = f.read_to_end(&mut bytes)?;
+    let s = std::str::from_utf8(&bytes)?;
+    Ok((n, s.to_string()))
+}
+
+fn main() {
+    match read_file_as_string("/tmp/file") {
+        Ok((n, s)) => {
+            println!("{}", n);
+            print!("{}", s);
+        }
+        Err(e) => {
+            println!("could not read /tmp/file: {}", e);
+            std::process::exit(1);
+        }
+    }
+}