started ch18.1

Characteristics of OO Languages.md

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 # Characteristics of Object-Oriented Languages
+
+There is no consensus about what features a language must have to be considered object-oriented.
+
+Rust is influenced by many programming paradigms, including OOP.
+
+Arguably, OOP languages share certain common characteristics, namely objects, encapsulations and ingeritance.
+
+Lets see what each of those means and whether Rust supports it.
+
+## Object Contain Data and Behavior
+
+The book _Design Patterns: Elements of Reusable Object-Oriented Software_ by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides (Addison-Wesley Professional, 1994).
+
+This is colloquially referred to as _The Gang of Four_ book, is a catalog of object-oriented design patters.
+
+It defines OOP as this:
+Object-oriented programs are made up of objects.
+An _object_ packages both data and the procedures that operate on that data.
+The procedures are typically called _methods_ or _operations_.
+Using this definition, Rust is object-oriented: structs and enumbs have data, and `impl` blocks provide methods on structs and enums.
+
+Even though structs and enums with methods aren't _called_ obejcts, they provide the same functionaliy accound to the Gang of Four's definition of objects.
+
+## Encapsulation that Hides Implementation Details
+
+An aspect commonly associated with OOP is the idea of _encapsulation_.
+
+This means that the implementation details of an object aren't accessible to code using that object.
+
+Therefore, the only way to interact with an object is through its public API.
+
+Code using the object shouldn't be able to reach into the object's internals and change data or behaviro directly.
+
+This enables the programmer to change and refactor an object's internals without needing to change the code that uses the object.
+
+We discussed previously how to control encapsulation in Ch7.
+
+We can use the `pub` keyword to decide which modules, types, function and methods in our code should be public .
+
+By default everything else is private.
+
+For example, if we defined a struct `AveragedCollection` that has a field containing a vector of `i32` values.
+
+The struct can also have a field that contains the average of te vlaues in the vector, meaning the average doesn't have to be computed on demand whenever anyone needs it.
+
+In other words, `AveragedCollection` will cache the calculated average of the values in the vector.
+
+Meaning the average doesn't have to be computed on demand whenever it is needed.
+
+`AveragedCollection` will cache the calculated average for us.
+
+Here is the definition of the `AveragedCollection` struct
+
+```rust
+pub struct AveragedCollection {
+    list: Vec<i32>,
+    average: f64,
+}
+```

hello_cargo/target/.rustc_info.json

@@ -1 +1 @@
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+{"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":{}}