This content originally appeared on DEV Community and was authored by Uday Yadav
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 variable
let f = square(5)
console.log(square)
console.log(f)
Passed as an Argument aka High order functions
// sqr the the passed square function
function 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 argument
let squares = my_map(square, [1, 2, 3, 4, 5, 6, 7])
console.log(squares)
Function as Return Type
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 outside
outer_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 and Mutable
// strings in js are immutable
// they cannot be changed once initialised
let name = "uday Yadav"
name[0] = "U";
// this makes not difference
console.log(name);
// still small case 'u'
console.log(name[0]);
// array in js is mutable
// they can be changed once created
let 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 name
console.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/
This content originally appeared on DEV Community and was authored by Uday Yadav
Uday Yadav | Sciencx (2021-07-25T07:40:10+00:00) SWE 101 : Programming Terms Explained in simplest form. Retrieved from https://www.scien.cx/2021/07/25/swe-101-programming-terms-explained-in-simplest-form/
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