initial commit and readme

Visitor Pattern/README.md

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+# Visitor Pattern
+
+> Allows you to define new operations without changing the classes of the elements on which they operate by separating the algorithm from the object structure.
+
+The Visitor design pattern is a behavioral pattern that enables you to add new operations to a set of related classes without altering their structure. It achieves this by separating the algorithm from the object structure. This is particularly useful when you have a complex object structure with different types of objects and you want to perform various operations on them without modifying their individual classes.
+
+Imagine you have a program that models a zoo with different types of animals: lions, monkeys, and giraffes. Each animal class has its own set of methods and properties. Now, let's say you want to perform various tasks on these animals, such as feeding, cleaning, and observing, without modifying the animal classes themselves.
+
+Here's where the Visitor pattern comes in handy. You can define a visitor interface with visit methods for each type of animal. Each animal class then implements an accept method that allows a visitor object to visit it. When you want to perform an operation on the animals, you create a concrete visitor class that implements the visitor interface and defines the behavior for each visit method.
+
+For example, you might have a FeedVisitor that implements visit methods for feeding each type of animal. When you want to feed all the animals in the zoo, you create an instance of the FeedVisitor and iterate over the list of animals, calling the accept method on each animal and passing the visitor object. Each animal then accepts the visitor, which in turn calls the appropriate visit method for that animal type, performing the feeding operation.
+
+This approach keeps the logic for each operation separate from the animal classes, making it easy to add new operations without modifying existing code. It also follows the open/closed principle, allowing you to extend the behavior of the program without altering its source code.
+
+## Application
+
+- an object structure contains many classes of objects with differing interfaces, and you want to perform operations on these objects that depend on their concrete classes.
+- many distinct and unrelated operations need to be performed on objects in an object structure, and you want to avoid "polluting" their classes with these operations. Visitor lets you keep related operations together by defining them in one class. When the object structure is shared by many applications, use Visitor to put operations in just those applications that need them.
+- the classes defining the object structure rarely change, but you often want to define new operations over the structure. Changing the object structure classes requires redefining the interface to all visitors, which is potentially costly. If the object structure classes change often, then it's probably better to define the operations in those classes.
+
+## Definitions
+
+**Visitor**
+: declares a Visit operation for each class of ConcreteElement in the object structure. The operation's name and signature identifies the class that sends the Visit request to the visitor. That lets the visitor determine the concrete class of the element being visited. Then the visitor can access the element directly through its particular interface.
+
+**Concrete Visitor**
+: implements each operation declared by Visitor. Each operation implements a fragment of the algorithm defined for the corresponding
+class of object in the structure. ConcreteVisitor provides the context for the algorithm and stores its local state. This state often accumulates results during the traversal of the structure.
+
+**Element**
+: defines an Accept operation that takes a visitor as an argument.
+
+**Concrete Element**
+: implements an Accept operation that takes a visitor as an argument.
+
+**Object Structure**
+: can enumerate its elements. It may provide a high-level interface to allow the visitor to visit its elements. It may either be a composite or a collection such as a list or a set.
+
+## Consequences
+
+1. _Adding new ConcreteElement classes is hard_
+ : The Visitor pattern makes it hard to add new subclasses of Element. Each new ConcreteElement gives rise to a new abstract operation on Visitor and a corresponding implementation in every ConcreteVisitor class. Sometimes a default implementation can be provided in
+ Visitor that can be inherited by most of the ConcreteVisitors, but this is the exception rather than the rule. So the key consideration in applying the Visitor pattern is whether you are mostly likely to change the algorithm applied over an object structure or the classes of objects that make up the structure. The Visitor class hierarchy can be difficult to maintain when new ConcreteElement classes are added frequently. In such cases, it's probably easier just to define operations on the classes that make up the structure. If the Element class hierarchy is stable, but you are continually adding operations or changing algorithms, then the Visitor pattern will help you
+ manage the changes.
+
+2. _Breaking Encapsulation_
+ : Visitor's approach assumes that the ConcreteElement interface is powerful enough to let visitors do their job. As a result, the pattern
+ often forces you to provide public operations that access an element's internal state, which may compromise its encapsulation.

Visitor Pattern/index.html

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+<!DOCTYPE html>
+<html lang="en">
+ <head>
+ <meta charset="UTF-8" />
+ <meta http-equiv="X-UA-Compatible" content="IE=edge" />
+ <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+ <title>Visitor Pattern</title>
+ <link rel="stylesheet" href="style.css" />
+ <script src="./dist/visitorPattern.js" defer></script>
+ </head>
+ <body></body>
+</html>

Visitor Pattern/style.css

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+* {
+ margin: 0;
+ padding: 0;
+ box-sizing: border-box;
+}
+
+:root {
+ --color-one: #9e788f;
+ --color-two: #a9b3ce;
+ --color-three: #7cdedc;
+ --color-four: #7284a8;
+ --color-five: #474954;
+}

Visitor Pattern/tsconfig.json

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+{
+ "compilerOptions": {
+ /* Visit https://aka.ms/tsconfig.json to read more about this file */
+
+ /* Projects */
+ // "incremental": true, /* Enable incremental compilation */
+ // "composite": true, /* Enable constraints that allow a TypeScript project to be used with project references. */
+ // "tsBuildInfoFile": "./", /* Specify the folder for .tsbuildinfo incremental compilation files. */
+ // "disableSourceOfProjectReferenceRedirect": true, /* Disable preferring source files instead of declaration files when referencing composite projects */
+ // "disableSolutionSearching": true, /* Opt a project out of multi-project reference checking when editing. */
+ // "disableReferencedProjectLoad": true, /* Reduce the number of projects loaded automatically by TypeScript. */
+
+ /* Language and Environment */
+ "target": "es2016" /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */,
+ // "lib": [], /* Specify a set of bundled library declaration files that describe the target runtime environment. */
+ // "jsx": "preserve", /* Specify what JSX code is generated. */
+ "experimentalDecorators": true /* Enable experimental support for TC39 stage 2 draft decorators. */,
+ // "emitDecoratorMetadata": true, /* Emit design-type metadata for decorated declarations in source files. */
+ // "jsxFactory": "", /* Specify the JSX factory function used when targeting React JSX emit, e.g. 'React.createElement' or 'h' */
+ // "jsxFragmentFactory": "", /* Specify the JSX Fragment reference used for fragments when targeting React JSX emit e.g. 'React.Fragment' or 'Fragment'. */
+ // "jsxImportSource": "", /* Specify module specifier used to import the JSX factory functions when using `jsx: react-jsx*`.` */
+ // "reactNamespace": "", /* Specify the object invoked for `createElement`. This only applies when targeting `react` JSX emit. */
+ // "noLib": true, /* Disable including any library files, including the default lib.d.ts. */
+ // "useDefineForClassFields": true, /* Emit ECMAScript-standard-compliant class fields. */
+
+ /* Modules */
+ "module": "commonjs" /* Specify what module code is generated. */,
+ "rootDir": "./src" /* Specify the root folder within your source files. */,
+ // "moduleResolution": "node", /* Specify how TypeScript looks up a file from a given module specifier. */
+ // "baseUrl": "./", /* Specify the base directory to resolve non-relative module names. */
+ // "paths": {}, /* Specify a set of entries that re-map imports to additional lookup locations. */
+ // "rootDirs": [], /* Allow multiple folders to be treated as one when resolving modules. */
+ // "typeRoots": [], /* Specify multiple folders that act like `./node_modules/@types`. */
+ // "types": [], /* Specify type package names to be included without being referenced in a source file. */
+ // "allowUmdGlobalAccess": true, /* Allow accessing UMD globals from modules. */
+ // "resolveJsonModule": true, /* Enable importing .json files */
+ // "noResolve": true, /* Disallow `import`s, `require`s or `<reference>`s from expanding the number of files TypeScript should add to a project. */
+
+ /* JavaScript Support */
+ // "allowJs": true, /* Allow JavaScript files to be a part of your program. Use the `checkJS` option to get errors from these files. */
+ // "checkJs": true, /* Enable error reporting in type-checked JavaScript files. */
+ // "maxNodeModuleJsDepth": 1, /* Specify the maximum folder depth used for checking JavaScript files from `node_modules`. Only applicable with `allowJs`. */
+
+ /* Emit */
+ // "declaration": true, /* Generate .d.ts files from TypeScript and JavaScript files in your project. */
+ // "declarationMap": true, /* Create sourcemaps for d.ts files. */
+ // "emitDeclarationOnly": true, /* Only output d.ts files and not JavaScript files. */
+ // "sourceMap": true, /* Create source map files for emitted JavaScript files. */
+ // "outFile": "./", /* Specify a file that bundles all outputs into one JavaScript file. If `declaration` is true, also designates a file that bundles all .d.ts output. */
+ "outDir": "./dist" /* Specify an output folder for all emitted files. */,
+ // "removeComments": true, /* Disable emitting comments. */
+ // "noEmit": true, /* Disable emitting files from a compilation. */
+ // "importHelpers": true, /* Allow importing helper functions from tslib once per project, instead of including them per-file. */
+ // "importsNotUsedAsValues": "remove", /* Specify emit/checking behavior for imports that are only used for types */
+ // "downlevelIteration": true, /* Emit more compliant, but verbose and less performant JavaScript for iteration. */
+ // "sourceRoot": "", /* Specify the root path for debuggers to find the reference source code. */
+ // "mapRoot": "", /* Specify the location where debugger should locate map files instead of generated locations. */
+ // "inlineSourceMap": true, /* Include sourcemap files inside the emitted JavaScript. */
+ // "inlineSources": true, /* Include source code in the sourcemaps inside the emitted JavaScript. */
+ // "emitBOM": true, /* Emit a UTF-8 Byte Order Mark (BOM) in the beginning of output files. */
+ // "newLine": "crlf", /* Set the newline character for emitting files. */
+ // "stripInternal": true, /* Disable emitting declarations that have `@internal` in their JSDoc comments. */
+ // "noEmitHelpers": true, /* Disable generating custom helper functions like `__extends` in compiled output. */
+ // "noEmitOnError": true, /* Disable emitting files if any type checking errors are reported. */
+ // "preserveConstEnums": true, /* Disable erasing `const enum` declarations in generated code. */
+ // "declarationDir": "./", /* Specify the output directory for generated declaration files. */
+ // "preserveValueImports": true, /* Preserve unused imported values in the JavaScript output that would otherwise be removed. */
+
+ /* Interop Constraints */
+ // "isolatedModules": true, /* Ensure that each file can be safely transpiled without relying on other imports. */
+ // "allowSyntheticDefaultImports": true, /* Allow 'import x from y' when a module doesn't have a default export. */
+ "esModuleInterop": true /* Emit additional JavaScript to ease support for importing CommonJS modules. This enables `allowSyntheticDefaultImports` for type compatibility. */,
+ // "preserveSymlinks": true, /* Disable resolving symlinks to their realpath. This correlates to the same flag in node. */
+ "forceConsistentCasingInFileNames": true /* Ensure that casing is correct in imports. */,
+
+ /* Type Checking */
+ "strict": true /* Enable all strict type-checking options. */,
+ // "noImplicitAny": true, /* Enable error reporting for expressions and declarations with an implied `any` type.. */
+ // "strictNullChecks": true, /* When type checking, take into account `null` and `undefined`. */
+ // "strictFunctionTypes": true, /* When assigning functions, check to ensure parameters and the return values are subtype-compatible. */
+ // "strictBindCallApply": true, /* Check that the arguments for `bind`, `call`, and `apply` methods match the original function. */
+ "strictPropertyInitialization": false, /* Check for class properties that are declared but not set in the constructor. */
+ // "noImplicitThis": true, /* Enable error reporting when `this` is given the type `any`. */
+ // "useUnknownInCatchVariables": true, /* Type catch clause variables as 'unknown' instead of 'any'. */
+ // "alwaysStrict": true, /* Ensure 'use strict' is always emitted. */
+ // "noUnusedLocals": true, /* Enable error reporting when a local variables aren't read. */
+ // "noUnusedParameters": true, /* Raise an error when a function parameter isn't read */
+ // "exactOptionalPropertyTypes": true, /* Interpret optional property types as written, rather than adding 'undefined'. */
+ // "noImplicitReturns": true, /* Enable error reporting for codepaths that do not explicitly return in a function. */
+ // "noFallthroughCasesInSwitch": true, /* Enable error reporting for fallthrough cases in switch statements. */
+ // "noUncheckedIndexedAccess": true, /* Include 'undefined' in index signature results */
+ // "noImplicitOverride": true, /* Ensure overriding members in derived classes are marked with an override modifier. */
+ // "noPropertyAccessFromIndexSignature": true, /* Enforces using indexed accessors for keys declared using an indexed type */
+ // "allowUnusedLabels": true, /* Disable error reporting for unused labels. */
+ // "allowUnreachableCode": true, /* Disable error reporting for unreachable code. */
+
+ /* Completeness */
+ // "skipDefaultLibCheck": true, /* Skip type checking .d.ts files that are included with TypeScript. */
+ "skipLibCheck": true /* Skip type checking all .d.ts files. */
+ }
+ }
+