Rust : Update.

dev/lang/rust/Error.md

@@ -0,0 +1,15 @@
+# Error.
+
+Replaces `Option<T>`.
+
+# Create.
+
+```rust
+fn foo() -> Result<String, String> {
+    if bar {
+        Err("Barrr!")
+    } else {
+        Ok("Foo!")
+    }
+}
+```

dev/lang/rust/Generics.md

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+# Rust generics.
+
+Generics in rust are similar to java's.
+
+# Definition.
+
+Function:
+
+```rust
+fn largest<T>(list: &[T]) -> &T {}
+```
+
+Struct:
+
+```rust
+struct Point<T> {
+	x: T,
+	y: T,
+}
+
+impl<T> Point<T> {
+	fn x(&self) -> &T {
+		&self.x
+	}
+}
+```
+
+Enum:
+
+```rust
+enum Result<T, E> {
+	Ok(T),
+	Err(E),
+}
+```
+
+

dev/lang/rust/Option.md

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+# Option.
+
+# Definition.
+
+```rust
+enum Option<T> {
+    None,
+    Some(T),
+}
+```
+
+# Usage.
+
+```rust
+fn maybe_icecream(hour: u16) -> Option<u16> {
+    if hour > 10 { Some(5) }
+    else { None }
+}
+```
+
+# Subtypes.
+
+## If-let.
+
+```rust
+let letter: Option<i32> = Some(12);
+if let Some(i) = letter {
+    // It was Some().
+} else {
+    // It was None.
+}
+```
+
+## While-let.
+
+```rust
+let letter: Option<i32> = Some(0);
+while let Some(i) = letter {
+    if i > 9 {
+        foo();
+        letter = None;
+    } else {
+        bar()
+        letter = Some(i + 1);
+    }
+}
+```
+
+## Match.
+
+Use `ref` keyword to borrow value that doesn't implement `Copy` trait.
+
+```rust
+let y: Option<Point> = Some(Point { x: 100, y: 200 });
+match y {
+    Some(ref p) => println!("Co-ordinates are {},{} ", p.x, p.y),
+    _           => panic!("no match!"),
+}
+```