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July 25, 2021 07:40 am GMT

SWE 101 : Programming Terms Explained in simplest form

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What is idempotent again ?

Closure, Memoization, Idempotence : Decoding and understanding programming terms one by one in simplest definition

All code written in this javascript, but dont worry about the language, syntax is kept super simple. For practise, you can implement them in your favourite programming language.

Lets start with first class functions

First Class Function

A programming language is said to have first class functions if it treat its functions as first class citizens

What are first class citizens : something that can be

  • passed as an argument
  • returned from a function
  • assigned to a variable

Whatever satisfies the above 3 properties in you programming language can be called as first class citizen. Lets take a look at with examples

Assigning Function to a variable

function square(x) {  return x * x } // Assigned to another variablelet f = square(5)      console.log(square) console.log(f)

Passed as an Argument aka High order functions

// sqr the the passed square functionfunction my_map(sqr, args) {    let result = []    for (let i = 0; i < args.length; i++) {        // the passed function is used here       result.push(sqr(args[i]))    }    return result; }// square function is passed as argumentlet squares = my_map(square, [1, 2, 3, 4, 5, 6, 7]) console.log(squares)

Function as ReturnType

function logger(msg) {    function log_message() {     console.log("Log : " + msg)    }    //  this is a function, returning from parent functions   return log_message } logHello = logger("hello") logHello()

Before moving on, please read the above and try to understand the concept, it would be helpfull

Closure

They are similar to functions returned from another function but captures the internal state of parent function at the time of invoked.

  • A closure is a record storing a function together with an environment, a mapping associating each free variable of the function with the value of storage location to which the name was bound when then the closure was created. ( Kinda formal, read below and look at code snippet )
  • A closure, unlike a plain function, allows the function to access those captured and closed variables when the function is invoked outside the scope.
function outer_function() {   message = "hello world"   function inner_function() {       console.log (message) // Look at point 2 from definition   }   return inner_function()}// invoked from outsideouter_function()

Another Example of Closure

function outer_function(msg) {   message = msg   function inner_function() {       console.log (message)   }   return inner_function}let func = outer_function("Hello World")func()

Immutable andMutable

// strings in js are immutable // they cannot be changed once initialisedlet name = "uday Yadav"name[0] = "U";// this makes not differenceconsole.log(name);// still small case 'u'console.log(name[0]); // array in js is mutable // they can be changed once createdlet data = [0,2,3,4];data[0] = 1;console.log(data);

Memoization

Some operations are expensive to preform, so we store the results of them in some form of temporary storage and when required to recalculate, first find them in the temporary storage.

let cache = {}function expensive_compute(data) {   if (cache.hasOwnProperty(data)) {       console.log("answer cache : "+cache[data])       cache[data] = data*data       return;   }   cache[data] = data*data   console.log("answer : "+cache[data])}expensive_compute(4)expensive_compute(10)expensive_compute(4)expensive_compute(16)expensive_compute(10)

Idempotence

The property of certain operations in mathematics and computer science, that can be applied multiple times without changing the result without initial application

function abs(number) {   if (number < 0) {       return -1 * number;   }   return number;}console.log(abs(-10));console.log(abs(10));console.log(abs(abs(-10)))

Not Idempotent example

function add_one(number) {   return number + 1;}console.log(add_one(-10));console.log(add_one(10));

Ephemeral

synonyms to temporary

Anonymous Functions

Function without a name, also known as lambda function in
Python

let arr = [1, 2, 3];let mapped = arr.map(x => Math.pow(x, 2));// x =>  is a function without a nameconsole.log(mapped);

Predicate

Functions that return true or false depending on the input. They usually start with is

class Animal {   constructor(_type) {       this.type = _type;   }}function makeSound(animal) {   if (isCat(animal)) {       console.log(" MEOW ! ");       return;   }   console.log(" NOT CAT ! ");}function isCat(animal) {   return animal.type === 'Cat';}let newCat = new Animal('Cat');makeSound(newCat);

Parsing and Stringify

  • Parsing: converting string to some object
  • Stringify: converting some object to string
let data = {   "name": "Uday Yadav",   "Gender": "Male"}let str = JSON.stringify(data)console.log(str + "|" + typeof str)let dataReturns = JSON.parse(str)console.log(dataReturns + "|" + typeof dataReturns)

More about me: https://uday-yadav.web.app/


Original Link: https://dev.to/dev117uday/swe-101-programming-terms-explained-in-simplest-form-401h

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