ch5 methods almost complete

data_types.md

@@ -453,4 +453,123 @@ struct User {
 }
 ```
 
-In short use data times that are owned rather than references
+In short use data times that are owned rather than references
+
+## Adding Increased Functionality of Structs with derived traits
+
+print can do many different types of formatting
+Cant print out structs by default because there are so many options
+with or without braces, commas, should all fields be shown
+This will cause an error
+```rust
+struct Rectangle {
+    length: u32,
+    width: u32,
+}
+    let rect1 = Rectangle {
+        length: 8,
+        width: 4,
+    };
+    println!("rect1 contains {}", rect1);
+```
+
+{} tell println to use Display by default because there is only one way to show many primitive data types
+
+{var_name:?} this is for the format Debug
+{var_name:#?} this is for pretty printing in Debug format, good for larger structs
+
+Debug is also not implemented for the struct and therefore not supported
+
+```rust
+#[derive(Debug)]
+struct Rectangle {
+    length: u32,
+    width: u32,
+}
+    // snip
+    println!("rect1 contains {rect1:?}");   // single line print, in debug format, output: rect1 contains Rectangle { length: 8, width: 4 }
+    println!("rect1 contains {rect1:#?}");  // pretty print in debug format, output: rect1 contains Rectangle {
+                                            // length: 8,
+                                            // width: 4,
+                                            // }
+```
+
+Another way to output pretty debug format by default is dbg! macro
+this prints out the file and line number as well of where it was called and returns the ownership of the value
+this prints to the stderr output stream
+this takes ownership of values compaired to println!
+prints to stdout output stream
+
+example of using dbg
+```rust
+fn main() {
+    let scale = 2;
+    let rect1 = Rectangle {
+        width: dbg!(30 * scale),
+        height: 50,
+    };
+    dbg!(&rect1); // because it takes ownership need to pass in a reference
+}
+```
+output
+[src/main.rs:10:16] 30 * scale = 60
+[src/main.rs:14:5] &rect1 = Rectangle {
+    width: 60,
+    height: 50,
+}
+
+## Methods
+Fucntions that are more closely related to structs
+
+similar to functions decalred, param and output are all the same
+
+run the code when the method is declared elsewhere
+
+unlike functions they are defined in the context of a struct, an enum or a trait
+
+first parameter is always self, which represents the instance of the struct that is is being called upon
+just like python methods
+
+definition
+```rust
+struct Rectangle {
+    length: u32,
+    width: u32,
+}
+
+// implementation block for Rectangle used to define fn related to the struct
+// put in this blcok so that the use case doesnt need to be searched
+impl Rectangle {
+    // fn moved to here to that it has access to the instance with the self reference
+    // fn now closely related to the rect struct
+    // first param must be the type self: Self or &self which rust lets you shorthand
+    // self can be borrowed, mutably borrowed, or take ownership of self
+    // should always borrow unless need to transferownership or mutate the stored var
+    // &mut self for mutable version of selfs
+    // use self when you want to transform the self into something else
+    fn area (&self) -> u32 {
+        self.length * self.width
+    }
+}
+```
+
+useage
+```rust
+    let rect1 = Rectangle {
+        length: 8,
+        width: 4,
+    }
+    println!("The area of the reactangle is {} square units",
+    // method syntax to call the area func
+    // notice dont need any param in, already has access to self reference
+    rect1.area()
+    );
+```
+
+this provides method syntax and dont have to repeat the structure they effect
+one impl can house all the methods for a struct, we can have tthe same method name as field name
+just differenitate with the use of () this is for a mthod not the field
+
+this is used in getters where you want read only access to a struct, you can make the field pravate but the method public
+
+130