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+Is in the prelude, so always available. Used where we can return something or none, instead of null.
+
+```rust
+enum Option<T> {
+  None
+  Some(T)
+}
+```
+
+This enables the compiler to check whether we handle both cases. Why?
+```rust
+fn do_something(int: i32, nope: bool) -> Option<i32> {
+	if (nope) {
+		return None
+	}
+
+	return Some(int * 2)
+}
+```
+
+The concrete return type is either `None` or `Some<i32>`: so if the called would for example do `1 + do_something(2, false);` would not compile because the return type is not an i32. Unlike for example PHP where it's `?int` so either `null` or `int` the compiler can't check this.
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