Hacker News Reader

Comment by _31 | Hacker News Reader

Great read!

I'm going to steal that use of 'typealias' when defining a closure that uses @escaping. Those method definitions are always so messy looking, this really cleans it up.

View on HN

Type alias is a poor alternative for true primitive types. Like (pseudo code):

    primitive Dollar: Decimal // no mixing with euros
    primitive Meter: Double // no confusion with miles

You can do the same in Swift with typealias _but_ it will happily accept you passing in Euro where Dollar is declared because they’re both Decimals. This doesn’t happen in languages like F#.

You can define a struct with a single field of type Double.

True. I think there was a Money cocoapod that used your trick. But you can’t do anything with them you would normally do with the base type unless you add a ton of logic.

Also in F# you get the type Meter/Hour if you divide Meters by Hours. Which multiplied by an Hour value gives you the distance traveled at that speed in that time.

Reply on news.ycombinator.com