finished ch7.2 and started ch7.3

Paths.md

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+# Paths
+
+## Paths for Referring to an Item in the Module Tree
+to show the rust compiler where to find an item in a module tree we use a path similar to navigating a filesystem, where the function is located
+
+A path can be two forms:
+- *Absolute path* - the full path starting from a crate root to the code of an external crate, the absolute path begins with the crate name and for code form the current crate it starts with the literal *crate*
+- *Relative path* - starts from the current module and uses ``self``, ``super``, or an identifier in the current module
+Both types of paths are followed by one or more identifiers separated by ``::``
+
+module tree for example
+```
+crate
+ └── front_of_house
+     ├── hosting
+     │   ├── add_to_waitlist
+     │   └── seat_at_table
+     └── serving
+         ├── take_order
+         ├── serve_order
+         └── take_payment
+```
+
+```rust
+    // Absolute path
+    crate::front_of_house::hosting::add_to_waitlist();
+
+    // Relative path
+    front_of_house::hosting::add_to_waitlist();
+```
+
+these are both calls to different parts of a different module from the parent crate named ``crate``
+this is equivalent to ``/front_of_house/hosting/add_to_waitlist`` in another language where the first ``/`` is the crate root or the ``./``
+
+choose the pathing based off your requirements/future organization of code
+preference is to specify absolute paths because more likely to move code definitions and item calls independently of each other
+
+rust will be able to tell the difference between a private function and a wrong path error
+
+any function, method, struct, enum, module and constants are private by default
+
+child modules can use parent modules but parent modules cannot use child modules
+
+child modules wrap their implementation to those above but not to itself or below
+
+you use pub keyword to expose to the parent module
+this is done so that you know what breaks your code
+
+this is valid and allows for the outermost crate to access the function add_to_watlist through the root defined front_of_house module
+```rust
+mod front_of_house {
+    pub mod hosting {
+        pub fn add_to_waitlist() {}
+    }
+}
+```
+
+it is called by ``crate::front_of_house::hosting::add_to_waitlist();``
+from the sister module/function
+if it was up another level then front_of_house would need a pub
+
+can be called by the relative path ``front_of_house::hosting::add_to_waitlist();``
+
+the public API that is determined by the developer is the contract with the users through other crates.
+There are many considerations to your public api to make it easier for people to depend on your crate
+These details and considerations are more concretely outlined in the [The Rust API Guidelines](https://rust-lang.github.io/api-guidelines/)