remove typo

subject_text/errors/options.md

@@ -0,0 +1,62 @@
+---
+name = "Options"
+file = "src/errors/option.rs"
+---
+
+Sometimes, a function can fail to compute a value simply because the value you asked simply does not exist. For example, when you try to access a collection at a wrong index, or when you want to divide by zero.
+
+To check for the existence or absence of value, we use the  `Option` type. `Option` by itself is not a type, but a generic type, meaning it needs to be annotated with an other type, like this: `Option<Type>`. This allow us to have `Option<i32>`, `Option<String>`, `Option<&str>` ... And even `Option<Option<i32>>` if you want (but this one is a bit weird and you won't encounter it often.
+
+`Option` comes in two flavors (named variants):
+
+- `None`, to encode the absence of value.
+- `Some(v)`, to encode the presence of value. Note the  `v` after `Some` to name the wrapped value.
+
+In order to create values of type `Option<T>`, we just name the variant we want, and if needed, we give the variant a value:
+
+```rust
+let some_one = Some(1);
+let nothing: Option<i32> = None;
+```
+
+To match against an `Option` value, you can use pattern matching:
+
+```rust
+let array = [1, 2, 3];
+let element: Option<&i32> = array.first();
+
+match element {
+    None => println!("array has no first value"),
+    Some(v) => println!("the first value is {}", v),
+}
+```
+
+In this part we will try to implement usual functions of `Option`:
+
+```prototype
+/// Returns `true` if `opt` is `Some`
+/// and `false` otherwise.
+pub fn is_some(opt: &Option<i32>) -> bool {
+    unimplemented!()
+}
+
+/// Returns the value wrapped in `opt` if it is `Some`,
+/// and `default` otherwise.
+pub fn get_or_default(opt: Option<i32>, default: i32) -> i32 {
+    unimplemented!()
+}
+
+/// Returns the value wrapped in `opt` if there is any,
+/// and panic!() otherwise.
+pub fn get_or_panic(opt: Option<i32>) -> i32 {
+    unimplemented!()
+}
+```
+
+```example
+fn main() {
+    dbg!(is_some(&None)); // false
+    dbg!(get_or_default(Some(5), 1)); // 5
+    dbg!(get_or_panic(Some(2))); // 2
+}
+```