harsh183

I've gotten many questions about this from both students, and current existing course staff since type inference is a reasonably new age concept that is getting picked up in the programming languages of the 2010s and 2020s.

The lesson gives a pretty good starting point, especially the 7-minute walkthrough here on the basics of type inference.

---

Talk is cheap, show me the code

I redid a few of the older problems using var type inference across a few of the past homework problems to see this in action. I highly suggest checking these out.

harsh183

// try this out on jeed playground at https://cs125.cs.illinois.edu/

interface TestCase {
  boolean test();
}
// print title if case fails
void checkCase(String title, TestCase t) {
  if (t.test() == false) {
    System.out.println("Failed: " + title);
  }

harsh183

// Linked list
data class Node<T>(var value: T, var next: Node<T>?);

fun main() {
  val head = Node(1, null)
  val second = Node(2, Node(3, null))   // two more (init multiple)
  head.next = second
  
  println(head.value)                   // 1
  println(head.next?.value)             // 2

harsh183

#!/usr/bin/env bash
set -ex

kotlinc $1 -d $1.jar
java -jar $1.jar

harsh183

fun main() {
    // Both are the same
    val array1: Array<Int> = arrayOf(0, 1, 4, 9, 16) 
    val list1: List<Int> = listOf(0, 1, 4, 9, 16)
    val map1: Map<Int, Int> = mapOf(0 to 0, 1 to 1, 2 to 4, 3 to 9, 4 to 16)
    
    val array2: Array<Int> = Array(5) { it*it }
    val list2: List<Int> = List(5) {it*it}
    val map2: Map<Int, Int> = (Array(5) {it}).associate {it to it*it}
}

harsh183

fun main() {
    // normal function
    repeat(3) { print("Yay $it ") }
    // => Yay 0 Yay 1 Yay 2 
  
    2.times { print("Looop ") }
    // => Looop Looop 
    10.times { print("$it ") }
    // => 0 1 2 3 4 5 6 7 8 9
}

harsh183

#include <iostream>
#include <string>
#include <vector>

#include <functional> // std::function, std::bind
#include <algorithm>  // std::transform, std::remove_if 
#include <numeric>    // std::accumulate

using namespace std;

harsh183

require 'pry'
require 'rqrcode'

qrcode = RQRCode::QRCode.new('https://cs125.cs.illinois.edu')

png = qrcode.as_png(
  bit_depth: 1,
  border_modules: 4,
  color_mode: ChunkyPNG::COLOR_GRAYSCALE,
  color: 'black',

harsh183

# Simple script I put together showing mypy in action 

# standard type annotations - we can give arguments a type and expect a return type
def add(x: int, y: int) -> int:
    return x + y 

print(add(1, 2))

# we can let it pick within a list of types
from typing import Union

harsh183

#!bin/bash

# This script is for me creating my brain dumps that I usually do jumping right into it in vim. 
# I have a template file also defined that I can setup if I want. 
# This script also brings me back to the same context that I was in earlier

set -ex

cd ~/brain-dumps/