finished ch18.1

Characteristics of OO Languages.md

@@ -58,3 +58,120 @@ pub struct AveragedCollection {
     average: f64,
 }
 ```
+
+This struct is marked `pub` os that other code can use it.
+
+The fields within the struct remain private.
+
+This is improtant becuase we want to ensure that whenever a value is added or removed from the lust, the average is also updated.
+
+We accomplish this by implementing `add`, `remove` and `average` methods on the struct.
+
+This is shown here
+
+```rust
+impl AveragedCollection {
+    pub fn add(&mut self, value: i32) {
+        self.list.push(value);
+        self.update_average();
+    }
+
+    pub fn remove(&mut self) -> Option<i32> {
+        let result = self.list.pop();
+        match result {
+            Some(value) => {
+                self.update_average();
+                Some(value)
+            }
+            None => None,
+        }
+    }
+
+    pub fn average(&self) -> f64 {
+        self.average
+    }
+
+    fn update_average(&mut self) {
+        let total: i32 = self.list.iter().sum();
+        self.average = total as f64 / self.list.len() as f64;
+    }
+}
+```
+
+The public methods, `add`, `remove` and `average` are the only ways to access or modify data in any instance of `AverageCollection`.
+
+When an item is added or removed to `list`, using the associated method, the implementations of each call the private `update_average` method that handles updating the `average` field as well.
+
+We leave the `list` and `average` fields private, so that there is no way for external code to add or remove items to or form the `list` field directly.
+
+The `average` method returns the value in the `average` field, this allows for external code to read the `average` but not modify it.
+
+Because we have encapsulated the impleentation details of `AveragedCollection`.
+
+We can easily change aspects, such as the data structure, in the future.
+
+For example, we could use a `HashSet<i32>` instead of a `Vec<i32>` for the `list` field.
+
+As long as the signatures of the `add`, `remove`, and `average` public methods stay the same.
+
+Code using `AveragedCollection` wouldn't need to change to order to compile.
+
+If we made `list` public instead, this wouldn't necessarily be the case
+
+`HashSet<i32>` and `Vec<i32>` have different methods for adding and removing items, so the external code would likely have to change if it were modifying `list` directly.
+
+If encapsulation is a required aspect for a language to be considered object-oriented, then Rust meets that requirement.
+
+The option to use `pub` or not for different parts of code enbalbes encapsulation of implementation details
+
+## Inheritance as a type System and as Code Sharing
+
+_Inheritance_ is a mechanism whereby an object can inherit elements from another obejct's definition, thus gaining the parent object's data and behavior without you having to define them again.
+
+If a language must have inheritance to be an obejct-oriented, then Rust is not one.
+
+There is no way to define a struct that inherits the parent struct fields and method implementations without using a macro.
+
+However, if you are use to having this tool available, you cna use other solutions in Rust, depending on your reason for reaching for inheritance.
+
+Yuo choose inheritance for main reasons.
+
+Resue of code: you can implement particular behavior for one type, and ingeritance enables ou to reuse that implementation for a different type.
+
+You can do this in a limited way in Rust ocde using default trait method implementations.
+
+We saw this before with the default implemetnation of the `summarize` method on the `Summary` trait.
+
+Any type implementing the `Summary` trait would have the `summarize` method available on it without any further code.
+
+This is similar to a parent class having an implementation of the `summarize` method when we `implement` the `Summary` trait, which is similar to a child class overriding the implementation of a method inherited form a parent class.
+
+The other resaon to use ingeritance relates to the type system: to enable a child to be used in the same place as the parent type.
+
+This has another name _polymorphism_, which means that you can substitute multiple objects for each other at runtime if they share certain characteristics.
+
+### Polymorphism
+
+    To many this is synonymous with inheritance.
+
+    But it is actually a more general concept that refers to code that can work with data of multiple tpyes.
+
+    For inheritance, those types are generally subclasses.
+
+    Rust instead use generics to abstract over different possible types and trait bounds to impose constraints on what those tpyes must provide.
+
+    This is sometimes called *bounded parametric polymorphism*.
+
+Inheritance has recently fallen out of favor as a programming deisgn solution, becuase it is often at risk of sharing more code than necessary.
+
+Subclasses shouldn't always share all characteristics of thier parent class but will do so with inheritance.
+
+This can make a program's design less flexible.
+
+This also introduces the possibility of calling methods on subclasses that don't make sense or that cause errors because the methods don't apply to the subclass.
+
+Additionally some languages will only allow single inheritance, meaning a subclass can only inherit from one class, thus further restricting the flexibility of a program's design.
+
+These reasons are why Rust takes the different approach of using trait objects instead of inheritance.
+
+Next lets see how trait obejcts enable polymorphism in Rust. [Here](./Trait%20Objects%20that%20allow%20for%20Values%20of%20Different%20Types.md)

Trait Objects that allow for Values of Different Types.md

@@ -0,0 +1 @@
+# Using Trait Objects That Allow for Values of Different Types

guessing_game/target/.rustc_info.json

@@ -1 +1 @@
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+{"rustc_fingerprint":953660965870803700,"outputs":{"13331785392996375709":{"success":true,"status":"","code":0,"stdout":"___\nlib___.rlib\nlib___.so\nlib___.so\nlib___.a\nlib___.so\n/home/brock/.rustup/toolchains/stable-x86_64-unknown-linux-gnu\noff\npacked\nunpacked\n___\ndebug_assertions\npanic=\"unwind\"\nproc_macro\ntarget_abi=\"\"\ntarget_arch=\"x86_64\"\ntarget_endian=\"little\"\ntarget_env=\"gnu\"\ntarget_family=\"unix\"\ntarget_feature=\"fxsr\"\ntarget_feature=\"sse\"\ntarget_feature=\"sse2\"\ntarget_has_atomic=\"16\"\ntarget_has_atomic=\"32\"\ntarget_has_atomic=\"64\"\ntarget_has_atomic=\"8\"\ntarget_has_atomic=\"ptr\"\ntarget_os=\"linux\"\ntarget_pointer_width=\"64\"\ntarget_vendor=\"unknown\"\nunix\n","stderr":""},"17747080675513052775":{"success":true,"status":"","code":0,"stdout":"rustc 1.85.1 (4eb161250 2025-03-15)\nbinary: rustc\ncommit-hash: 4eb161250e340c8f48f66e2b929ef4a5bed7c181\ncommit-date: 2025-03-15\nhost: x86_64-unknown-linux-gnu\nrelease: 1.85.1\nLLVM version: 19.1.7\n","stderr":""},"2063776225603076451":{"success":true,"status":"","code":0,"stdout":"___\nlib___.rlib\nlib___.so\nlib___.so\nlib___.a\nlib___.so\n/home/brock/.rustup/toolchains/stable-x86_64-unknown-linux-gnu\noff\npacked\nunpacked\n___\ndebug_assertions\npanic=\"unwind\"\nproc_macro\ntarget_abi=\"\"\ntarget_arch=\"x86_64\"\ntarget_endian=\"little\"\ntarget_env=\"gnu\"\ntarget_family=\"unix\"\ntarget_feature=\"fxsr\"\ntarget_feature=\"sse\"\ntarget_feature=\"sse2\"\ntarget_has_atomic=\"16\"\ntarget_has_atomic=\"32\"\ntarget_has_atomic=\"64\"\ntarget_has_atomic=\"8\"\ntarget_has_atomic=\"ptr\"\ntarget_os=\"linux\"\ntarget_pointer_width=\"64\"\ntarget_vendor=\"unknown\"\nunix\n","stderr":""}},"successes":{}}

hello_cargo/target/.rustc_info.json

@@ -1 +1 @@
-{"rustc_fingerprint":953660965870803700,"outputs":{"17747080675513052775":{"success":true,"status":"","code":0,"stdout":"rustc 1.85.1 (4eb161250 2025-03-15)\nbinary: rustc\ncommit-hash: 4eb161250e340c8f48f66e2b929ef4a5bed7c181\ncommit-date: 2025-03-15\nhost: x86_64-unknown-linux-gnu\nrelease: 1.85.1\nLLVM version: 19.1.7\n","stderr":""},"13331785392996375709":{"success":true,"status":"","code":0,"stdout":"___\nlib___.rlib\nlib___.so\nlib___.so\nlib___.a\nlib___.so\n/home/brock/.rustup/toolchains/stable-x86_64-unknown-linux-gnu\noff\npacked\nunpacked\n___\ndebug_assertions\npanic=\"unwind\"\nproc_macro\ntarget_abi=\"\"\ntarget_arch=\"x86_64\"\ntarget_endian=\"little\"\ntarget_env=\"gnu\"\ntarget_family=\"unix\"\ntarget_feature=\"fxsr\"\ntarget_feature=\"sse\"\ntarget_feature=\"sse2\"\ntarget_has_atomic=\"16\"\ntarget_has_atomic=\"32\"\ntarget_has_atomic=\"64\"\ntarget_has_atomic=\"8\"\ntarget_has_atomic=\"ptr\"\ntarget_os=\"linux\"\ntarget_pointer_width=\"64\"\ntarget_vendor=\"unknown\"\nunix\n","stderr":""},"2063776225603076451":{"success":true,"status":"","code":0,"stdout":"___\nlib___.rlib\nlib___.so\nlib___.so\nlib___.a\nlib___.so\n/home/brock/.rustup/toolchains/stable-x86_64-unknown-linux-gnu\noff\npacked\nunpacked\n___\ndebug_assertions\npanic=\"unwind\"\nproc_macro\ntarget_abi=\"\"\ntarget_arch=\"x86_64\"\ntarget_endian=\"little\"\ntarget_env=\"gnu\"\ntarget_family=\"unix\"\ntarget_feature=\"fxsr\"\ntarget_feature=\"sse\"\ntarget_feature=\"sse2\"\ntarget_has_atomic=\"16\"\ntarget_has_atomic=\"32\"\ntarget_has_atomic=\"64\"\ntarget_has_atomic=\"8\"\ntarget_has_atomic=\"ptr\"\ntarget_os=\"linux\"\ntarget_pointer_width=\"64\"\ntarget_vendor=\"unknown\"\nunix\n","stderr":""}},"successes":{}}
+{"rustc_fingerprint":953660965870803700,"outputs":{"13331785392996375709":{"success":true,"status":"","code":0,"stdout":"___\nlib___.rlib\nlib___.so\nlib___.so\nlib___.a\nlib___.so\n/home/brock/.rustup/toolchains/stable-x86_64-unknown-linux-gnu\noff\npacked\nunpacked\n___\ndebug_assertions\npanic=\"unwind\"\nproc_macro\ntarget_abi=\"\"\ntarget_arch=\"x86_64\"\ntarget_endian=\"little\"\ntarget_env=\"gnu\"\ntarget_family=\"unix\"\ntarget_feature=\"fxsr\"\ntarget_feature=\"sse\"\ntarget_feature=\"sse2\"\ntarget_has_atomic=\"16\"\ntarget_has_atomic=\"32\"\ntarget_has_atomic=\"64\"\ntarget_has_atomic=\"8\"\ntarget_has_atomic=\"ptr\"\ntarget_os=\"linux\"\ntarget_pointer_width=\"64\"\ntarget_vendor=\"unknown\"\nunix\n","stderr":""},"2063776225603076451":{"success":true,"status":"","code":0,"stdout":"___\nlib___.rlib\nlib___.so\nlib___.so\nlib___.a\nlib___.so\n/home/brock/.rustup/toolchains/stable-x86_64-unknown-linux-gnu\noff\npacked\nunpacked\n___\ndebug_assertions\npanic=\"unwind\"\nproc_macro\ntarget_abi=\"\"\ntarget_arch=\"x86_64\"\ntarget_endian=\"little\"\ntarget_env=\"gnu\"\ntarget_family=\"unix\"\ntarget_feature=\"fxsr\"\ntarget_feature=\"sse\"\ntarget_feature=\"sse2\"\ntarget_has_atomic=\"16\"\ntarget_has_atomic=\"32\"\ntarget_has_atomic=\"64\"\ntarget_has_atomic=\"8\"\ntarget_has_atomic=\"ptr\"\ntarget_os=\"linux\"\ntarget_pointer_width=\"64\"\ntarget_vendor=\"unknown\"\nunix\n","stderr":""},"17747080675513052775":{"success":true,"status":"","code":0,"stdout":"rustc 1.85.1 (4eb161250 2025-03-15)\nbinary: rustc\ncommit-hash: 4eb161250e340c8f48f66e2b929ef4a5bed7c181\ncommit-date: 2025-03-15\nhost: x86_64-unknown-linux-gnu\nrelease: 1.85.1\nLLVM version: 19.1.7\n","stderr":""}},"successes":{}}