comments

.vscode/settings.json

@@ -0,0 +1,6 @@
+{
+  "files.associations": {
+    "system_error": "cpp",
+    "xlocale": "cpp"
+  }
+}

README.md

@@ -14,13 +14,14 @@ Lessons:
 - [instanciating objects, accessing attributes and methods](./lessons/Instances.md)
 - [creating a class](./lessons/Classes.md)
 - [constructors](./lessons/Constructors.md)
+- [encapsulation](./lessons/Encapsulation.md)
+- [inheritance](./lessons/Inheritance.md)
+- [properties](./lessons/Properties.md)
+- [polymorphism](./lessons/Polymorphism.md)
 
 Work in progress:
 
-- inheritance
-- encapsulation
-- getter / setter / property
-- polymorphism
 - virtual classes
 - interfaces
 - Factories
+- Generics

cpp/Polymorphism.md

@@ -0,0 +1,5 @@
+# Polymorphism
+
+Relevant files:
+
+- [main.cpp](./inheritance/main.cpp)

cpp/inheritance/README.md

@@ -0,0 +1,13 @@
+# Inheritance
+
+c++ also allows to inherit from multiple base classes at once, but that is a
+little to complicated for this lesson.
+
+Relevant files:
+
+- [animal.h](./animal.h)
+- [animal.cpp](./animal.cpp)
+- [cat.h](./cat.h)
+- [cat.cpp](./cat.cpp)
+- [dog.h](./dog.h)
+- [dog.cpp](./dog.cpp)

cpp/inheritance/animal.cpp

@@ -0,0 +1,11 @@
+#include "animal.h"
+#include <iostream>
+#include <string>
+
+animal::animal(std::string name) {
+  this->name = name;
+}
+
+void animal::make_sound() {
+  cout << name << ":" << endl;
+}

cpp/inheritance/animal.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <string>
+using namespace std;
+
+class animal
+{
+  public:
+    std::string name;
+    // define make_sound as virtual to allow overriding in subclasses
+    virtual void make_sound();
+    animal(std::string name);
+};

cpp/inheritance/cat.cpp

@@ -0,0 +1,12 @@
+#include "cat.h"
+
+#include <iostream>
+#include <string>
+
+void cat::make_sound() {
+  // call the base class function first
+  animal::make_sound();
+
+  // add additional functionality
+  cout << "meow" << endl;
+}

cpp/inheritance/cat.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <string>
+// include the animal header
+#include "animal.h"
+using namespace std;
+
+// make the class inherit from animal
+class cat: public animal
+{
+  // include the animal constructor
+  using animal::animal;
+  public:
+    // override the make_sound function
+    void make_sound() override;
+};

cpp/inheritance/dog.cpp

@@ -0,0 +1,10 @@
+#include "dog.h"
+
+#include <iostream>
+#include <string>
+
+void dog::make_sound() {
+  // implement own functionality
+  cout << "doggo " << name << " says:" << endl;
+  cout << "woof!" << endl;
+}

cpp/inheritance/dog.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <string>
+// include the animal header
+#include "animal.h"
+using namespace std;
+
+// make the class inherit from animal
+class dog: public animal
+{
+  // include the animal constructor
+  using animal::animal;
+  public:
+    // override the make_sound function
+    void make_sound() override;
+};

cpp/inheritance/main.cpp

@@ -0,0 +1,17 @@
+#include "animal.h"
+#include "cat.h"
+#include "dog.h"
+
+#include <string>
+
+int main() {
+  // because cat and dog are subclasses of animal, they can be stored in an array of animals
+  animal * animals[2] = {
+    new dog("buster"),
+    new cat("mittens")
+  };
+
+  for (animal * a : animals)
+    // when calling the make_sound function, the implementation of the actual class gets called (in this case cat or dog)
+    a->make_sound();
+}

java/Polymorphism.md

@@ -0,0 +1,5 @@
+# Polymorphism
+
+Relevant files
+
+- [Program.java](./inheritance/Program.java)

java/inheritance/Animal.java

@@ -0,0 +1,11 @@
+public class Animal {
+  public String name;
+
+  public Animal(String name) {
+    this.name = name;
+  }
+
+  public void make_sound() {
+    System.out.println(this.name + ":");
+  }
+}

java/inheritance/Cat.java

@@ -0,0 +1,17 @@
+// make the class cat inherit from Animal
+public class Cat extends Animal {
+  // java requires an explicit constructor when the supertype awaits parameters in the constructor
+  public Cat(String name) {
+    // call supertype constructor
+    super(name);
+  }
+
+  // override make_sound
+  public void make_sound() {
+    // optional: call the parent class function
+    super.make_sound();
+
+    // add additional functionality
+    System.out.println("meow");
+  }
+}

java/inheritance/Dog.java

@@ -0,0 +1,14 @@
+public class Dog extends Animal {
+  // java requires an explicit constructor when the supertype awaits parameters in the constructor
+  public Dog(String name) {
+    // call supertype constructor
+    super(name);
+  }
+
+  // override the method make_sound
+  public void make_sound() {
+    // implement own functionality
+    System.out.println("doggo " + this.name + " says:");
+    System.out.println("woof!");
+  }
+}

java/inheritance/Program.java

@@ -0,0 +1,14 @@
+public class Program {
+  public static void main(String[] args) {
+    // because cat and dog are subclasses of animal, they can be stored in an array of animals
+    Animal[] animals = { 
+      new Dog("buster"), 
+      new Cat("mittens") 
+    };
+
+    for (Animal a : animals) {
+      // when calling the make_sound function, the implementation of the actual class gets called (in this case cat or dog)
+      a.make_sound();
+    }
+  }
+}

java/inheritance/README.md

@@ -0,0 +1,7 @@
+# Inheritance
+
+Relevant files:
+
+- [Animal.java](./Animal.java)
+- [Cat.java](./Cat.java)
+- [Dog.java](./Dog.java)

lessons/Encapsulation.md

@@ -0,0 +1,32 @@
+# Encapsulation
+
+Encapsulation is a simple lesson, this one is not gonna need any code examples.
+
+There are typically 3 keywords you need for encapsulation: private, protected
+and public.
+
+## Private
+
+Private methods and fields are only acessible from within the same class, they
+can't be read or written from outside.
+
+## Protected
+
+Protected is just like private, but descendant classes can access them.
+
+## Public
+
+Public is accessible from anywhere.
+
+## The static modifier
+
+Static is another one of those keywords, although it doesn't really control
+access to fields and methods. Anything with the static keyword can be used
+without an instance of the class. That means you can directly access with with
+Class.property instead of creating an instance of that class first. This is used
+for example in java for the main method, since it needs to be accessible without
+running any of the programs code first.
+
+Encapsulation is not a safety feature, it's only to make clear, which properties
+should be used by others. Methods like reflection and directly reading/writing
+memory can still access private or protected properties.

lessons/Inheritance.md

@@ -0,0 +1,15 @@
+# Inheritance
+
+Inheritance is useful to minimize code duplicates and generalize types in base
+classes.
+
+A Class can inherit all public and protected functions and fields from a base
+class and add its own or override existing ones. Private fields and functions
+still exist in the base class, but can't be acessed from the extending class.
+
+## Examples
+
+- [Java](../java/inheritance/README.md)
+- [Rust](../rust/Inheritance.md)
+- [C++](../cpp/inheritance/README.md)
+- [JavaScript (using TypeScript)](../typescript/inheritance/README.md)

lessons/Polymorphism.md

@@ -0,0 +1,19 @@
+# Polymorphism
+
+Polymorphism is the ability to treat subclasses like their base classes, for
+example passing cat, which extends animal to a function that expects an animal
+as parameter. or storing objects of different types that all extend a common
+class in an array of that common type.
+
+You lose acess to the properties of the subclass, but you can still access the
+base class like usual. When the subclass overrides behaviour of the base class,
+the overridden functionality in the subclass is still called.
+
+You can regain access to properties of the subclass with casting, but you have
+to make sure that the object is actually an instance of that class or you might
+run into runtime errors.
+
+- [Java](../java/Polymorphism.md)
+- [Rust](../rust/Inheritance.md)
+- [C++](../cpp/Polymorphism.md)
+- [JavaScript (using TypeScript)](../typescript/Polymorphism.md)

lessons/Properties.md

@@ -0,0 +1,61 @@
+# Properties
+
+Properties are a way to restrict read/write access to a field and to add
+additional verifications, computations or function calls to accessing a field.
+
+To define a property you need one private field that stores your data and the
+getter/setter for it. If you don't want it to be readable or writable, you can
+leave out either of the accessor functions.
+
+None of the languages featured here have a full implementation of properties.
+Languages like c# and Delphi do though.
+
+Delphi has the simplest syntax for properties I've seen so far.
+
+```pas
+  // this property will read from the field FFoo and write using the function set_foo
+  property Foo read FFoo write set_foo;
+```
+
+C# is a bit more complicated, but still better than the languages here
+
+```cs
+  public string Foo
+  {
+    get => _foo;
+    set {
+      _foo = do_something(value);
+    }
+  }
+```
+
+## Typescript
+
+Typescript allows a somewhat property implementation. In the class itself you
+define getter and setter functions using the get and set keywords
+
+```ts
+public get foo(): string {
+  return this._foo;
+}
+
+public set foo(val: string): void {
+  this._foo = do_something(val);
+}
+```
+
+From the outside, the property can be read and written like in c# and Delphi,
+just like working with a variable.
+
+## C++, Java and Rust
+
+Those languages don't provide a property syntax at all, instead you have to
+create public functions like set_foo and get_foo to replace them.
+
+## Additional note to rust
+
+Properties don't exist in rust either. But replacing them with getters and
+setters is also discouraged. Quoting from a reddit post
+`Expose behavior, not state`. That means you should present functions to outside
+viewers and not your plain data. An object should be able to do all its intended
+functions itself without having an outside observer read or write its data.

rust/Inheritance.md

@@ -0,0 +1,6 @@
+# Inheritance and Polymorphism
+
+Rust does not allow extending classes. Instead the base class is stored as a
+field in the extending class. Polymorphism can then be achieved by passing the
+field instead of the whole object to a function. Although casting back to the
+advanced class or overriding functions is not possible.

typescript/Polymorphism.md

@@ -0,0 +1,5 @@
+# Polymorphism
+
+Relevant files
+
+- [index.ts](./inheritance/index.ts)

typescript/inheritance/README.md

@@ -0,0 +1,7 @@
+# Inheritance
+
+Relevant files:
+
+- [animal.ts](./animal.ts)
+- [cat.ts](./cat.ts)
+- [dog.ts](./dog.ts)

typescript/inheritance/animal.ts

@@ -0,0 +1,11 @@
+export class Animal {
+  public name: string;
+
+  public constructor(name: string) {
+    this.name = name;
+  }
+
+  public make_sound() {
+    console.log(`${this.name}:`);
+  }
+}

typescript/inheritance/cat.ts

@@ -0,0 +1,13 @@
+import {Animal} from './animal';
+
+// make the class cat inherit from Animal
+export class Cat extends Animal {
+  // override make_sound
+  public make_sound() {
+    // optional: call the parent class function
+    super.make_sound();
+
+    // add additional functionality
+    console.log('meow');
+  }
+}

typescript/inheritance/dog.ts

@@ -0,0 +1,11 @@
+import {Animal} from './animal';
+
+export class Dog extends Animal {
+
+  // override the method make_sound
+  public make_sound() {
+    // implement own functionality
+    console.log(`doggo ${this.name} says:`);
+    console.log('woof!');
+  }
+}

typescript/inheritance/index.ts

@@ -0,0 +1,14 @@
+import { Dog } from "./dog";
+import { Cat } from "./cat";
+import { Animal } from "./animal";
+
+// because cat and dog are subclasses of animal, they can be stored in an array of animals
+const animals: Animal[] = [
+  new Dog('buster'),
+  new Cat('mittens')
+]
+
+for (const a of animals) {
+  // when calling the make_sound function, the implementation of the actual class gets called (in this case cat or dog)
+  a.make_sound();
+}

typescript/inheritance/package.json

@@ -0,0 +1,11 @@
+{
+  "name": "ts-oop",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "author": "",
+  "license": "ISC"
+}

typescript/inheritance/tsconfig.json

@@ -0,0 +1,66 @@
+{
+  "compilerOptions": {
+    /* Basic Options */
+    // "incremental": true,                   /* Enable incremental compilation */
+    "target": "es5",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
+    "module": "commonjs",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 'es2020', or 'ESNext'. */
+    // "lib": [],                             /* Specify library files to be included in the compilation. */
+    // "allowJs": true,                       /* Allow javascript files to be compiled. */
+    // "checkJs": true,                       /* Report errors in .js files. */
+    // "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
+    // "declaration": true,                   /* Generates corresponding '.d.ts' file. */
+    // "declarationMap": true,                /* Generates a sourcemap for each corresponding '.d.ts' file. */
+    // "sourceMap": true,                     /* Generates corresponding '.map' file. */
+    // "outFile": "./dist",                       /* Concatenate and emit output to single file. */
+    "outDir": "./dist",                        /* Redirect output structure to the directory. */
+    // "rootDir": "./",                       /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
+    // "composite": true,                     /* Enable project compilation */
+    // "tsBuildInfoFile": "./",               /* Specify file to store incremental compilation information */
+    // "removeComments": true,                /* Do not emit comments to output. */
+    // "noEmit": true,                        /* Do not emit outputs. */
+    // "importHelpers": true,                 /* Import emit helpers from 'tslib'. */
+    // "downlevelIteration": true,            /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
+    // "isolatedModules": true,               /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */
+
+    /* Strict Type-Checking Options */
+    "strict": true,                           /* Enable all strict type-checking options. */
+    // "noImplicitAny": true,                 /* Raise error on expressions and declarations with an implied 'any' type. */
+    // "strictNullChecks": true,              /* Enable strict null checks. */
+    // "strictFunctionTypes": true,           /* Enable strict checking of function types. */
+    // "strictBindCallApply": true,           /* Enable strict 'bind', 'call', and 'apply' methods on functions. */
+    // "strictPropertyInitialization": true,  /* Enable strict checking of property initialization in classes. */
+    // "noImplicitThis": true,                /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "alwaysStrict": true,                  /* Parse in strict mode and emit "use strict" for each source file. */
+
+    /* Additional Checks */
+    // "noUnusedLocals": true,                /* Report errors on unused locals. */
+    // "noUnusedParameters": true,            /* Report errors on unused parameters. */
+    // "noImplicitReturns": true,             /* Report error when not all code paths in function return a value. */
+    // "noFallthroughCasesInSwitch": true,    /* Report errors for fallthrough cases in switch statement. */
+
+    /* Module Resolution Options */
+    // "moduleResolution": "node",            /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
+    // "baseUrl": "./",                       /* Base directory to resolve non-absolute module names. */
+    // "paths": {},                           /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
+    // "rootDirs": [],                        /* List of root folders whose combined content represents the structure of the project at runtime. */
+    // "typeRoots": [],                       /* List of folders to include type definitions from. */
+    // "types": [],                           /* Type declaration files to be included in compilation. */
+    // "allowSyntheticDefaultImports": true,  /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
+    "esModuleInterop": true,                  /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
+    // "preserveSymlinks": true,              /* Do not resolve the real path of symlinks. */
+    // "allowUmdGlobalAccess": true,          /* Allow accessing UMD globals from modules. */
+
+    /* Source Map Options */
+    // "sourceRoot": "",                      /* Specify the location where debugger should locate TypeScript files instead of source locations. */
+    // "mapRoot": "",                         /* Specify the location where debugger should locate map files instead of generated locations. */
+    // "inlineSourceMap": true,               /* Emit a single file with source maps instead of having a separate file. */
+    // "inlineSources": true,                 /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */
+
+    /* Experimental Options */
+    // "experimentalDecorators": true,        /* Enables experimental support for ES7 decorators. */
+    // "emitDecoratorMetadata": true,         /* Enables experimental support for emitting type metadata for decorators. */
+
+    /* Advanced Options */
+    "forceConsistentCasingInFileNames": true  /* Disallow inconsistently-cased references to the same file. */
+  }
+}