TypeScript 2.4

Post by victorNicollet » Wed, Jun 28, 2017, 11:31 AM UTC

dotancohen wrote: post #31

Analemma_ wrote: post #29

Earlier quoted context omitted.

I would love for an ELI5 explanation of covariance/contravariance, but I've never seen one. I get it now, but only after reading and rereading explanations very carefully.

So, then how would you explain it to a five year old?

Explaining it to a five-year-old adds overhead that isn't really useful when you're in fact explaining to someone who knows about programming but has simply never heard about covariance and contravariance.

A function `X -> string` can be turned into a function `X -> object`: call it, take its string result and cast it to object. This is called covariant (latin co- for "together") because casting `string` to `object` also lets you cast `X -> string` to `X -> object`.

A function `object -> X` can turned into a function `string -> X`: take the string argument, cast it to object, and pass it to the function. This is called contravariant (latin contra- for "against") because casting `string` to `object` lets you cast `object -> X` to `string -> X`.

Post by dotancohen » Thu, Jun 29, 2017, 5:39 AM UTC

victorNicollet wrote: post #51

dotancohen wrote: post #31

Earlier quoted context omitted.

So, then how would you explain it to a five year old?

Explaining it to a five-year-old adds overhead that isn't really useful when you're in fact explaining to someone who knows about programming but has simply never heard about covariance and contravariance. A function `X -> string` can be turned into a function `X -> object`: call it, take its string result and cast it to object. This is called covariant (latin co- for "together") because casting `string` to `object`…

Thanks, obviously your example is more concrete. GP's comment was good for introducing the idea and your comment is great for showing how the idea is useful.

Re: TypeScript 2.4

Re: TypeScript 2.4