finished ch 6.2

.obsidian/workspace.json

@@ -179,15 +179,15 @@
   },
   "active": "bda58467a9a0a34e",
   "lastOpenFiles": [
-    "README.md",
-    "data_types.md",
-    "Untitled.canvas",
-    "ownership.md",
-    "Variables.md",
     "Data Types.md",
-    "Constants.md",
+    "data_types.md",
+    "Primitives.md",
+    "ownership.md",
     "Enums.md",
-    "Structures.md",
+    "Variables.md",
-    "Primitives.md"
+    "README.md",
+    "Untitled.canvas",
+    "Constants.md",
+    "Structures.md"
   ]
 }

data_types.md

@@ -851,3 +851,69 @@ then it would print out State quarter from Alaska
 because that is the only pattern that matches 
 
 ## Matching with Option T
+
+this can be done
+
+here is an example
+where there is a function that adds 1 to a non-null type and returns a null type if it is null
+```rust
+    fn plus_one(x: Option<i32>) -> Option<i32> {
+        match x {
+            None => None, // the null part
+            // i binds to the value inside Option i32
+            Some(i) => Some(i + 1), // the non-null part
+        }
+    }
+
+    let five = Some(5);
+    let six = plus_one(five);
+    let none = plus_one(None);
+```
+
+this handles both the None case and the not-null case
+
+very common pattern in rust to combine enums and matches then binding to the value inside
+
+very useful for when a range of data types are included
+
+## Matches are Exhaustive
+Matches must cover all possibilities
+there must be an arm for each pattern that could possibly come into contact with it
+if you don't he compiler will give an error
+
+all matches must exist therefore making matches exhaustive by default
+
+## Catch All Patterns and _ Placeholder
+
+for example lets say you have a game where if you roll a 3 you add a fancy hat and if you roll a 7 you remove a fancy hat and all other rolls result in the player moving
+
+it would look something like this
+```rust
+    let dice_roll = 9;
+    match dice_roll {
+	    // can do specific numbers as the pattern
+        3 => add_fancy_hat(),
+        7 => remove_fancy_hat(),
+        // this is allowed as a catch all this matches against all patterns not listed
+        // should go last in the case that it matches all patterns (including 3 and 7)
+        other => move_player(other),
+    }
+
+    fn add_fancy_hat() {}
+    fn remove_fancy_hat() {}
+    fn move_player(num_spaces: u8) {}
+```
+this uses a variable named other not a keyword
+this will match
+this catch all of other will satisfy the exhaustive requirements of match
+catch all must be last, rust will give a warning if this the wrong order and it will never run
+
+if we want to catch all but not use the value do _
+this matches to all values and does not blind to that value
+this is like ignoring all other values not found in this arm
+
+if you want nothing to happen from the ignore all then return a unit type from the match
+
+for example the arm _ => () does this, this should not be used in the case of a match trying to return something
+
+# If Let