Control Flow Analysis

[ashen tundra]

I'm fighting with typescript at a place where it's showing a control flow analysis based error.

while (foo === "apple") {
  changeFooToPear()
  while (foo === "pear") {
    makeFood()
    break
  }
}

I know that foo is changed to pear... so I'm fighting typescript. I'm here to ask, if typescript is trying to help me write better code, what is the clean solution?

[eager scaffold]

typescript kinda assumes functions are pure in this way, there's an issue for it somewhere

https://github.com/microsoft/TypeScript/issues/9998

[willow mason]

The easiest workaround is to use a function:

let foo: "apple" | "pear" = "apple";
// Using a function avoids TS from 'remembering' the narrowed value
const getFoo = () => foo;

while (getFoo() === "apple") {
  changeFooToPear()
  while (getFoo() === "pear") {
    makeFood()
    break
  }
}

[storm yacht]

the easiest workaround is to not mutate/reassign anything ever 😏