Discussion on: Daily Challenge #312 - Describe the Function

[Mihail Malo]

JavaScript

stupidly golfed:

calc_type=(a,b,c)=>[...'+-*/'].find(x=>eval(a+x+b+'=='+c))

reasonable:

const ops = '+-*/'.split('').map(x => [x, new Function('a', 'b', 'c', `return (a ${x} b) === c`)])
const calc_type = (a, b, c) => ops.find(([x,f]) => f(a,b,c))?.[0]

optimized:

function calc_type(a, b, c) {
  switch (c) {
    case a + b: return '+'
    case a - b: return '-'
    case a * b: return '*'
    case a / b: return '/'
  }
}

Guess what, flow control is expensive! Inlining saves the day, and case is number one.

Both of these are slower, despite not having to calculate the "expensive" division operation:

const ops = [
  (a, b) => a + b,
  (a, b) => a - b,
  (a, b) => a * b,
  (a, b) => a / b,
]
const calc_type = (a, b, c) => strs[ops.findIndex(f => f(a, b) === c)]

const ops = [
  (a, b, c) => (a + b) === c,
  (a, b, c) => (a - b) === c,
  (a, b, c) => (a * b) === c,
  (a, b, c) => (a / b) === c,
]
const calc_type = (a, b, c) => strs[ops.findIndex(f => f(a, b, c))]