Type syntax in destructured arguments of ES6 functions

[volkanunsal]

Say I have a function that looks like this:

var myfunction = ({a: string, b:string})=>{ ... }

When I run this through the transpiler, it complains that I'm using the same argument twice in strict mode –– I assume that's a reference to string. Obviously, the flow syntax is not working here. I am wondering how I should type the destructured arguments to make it work. I suppose I could just remove the strict mode pragma.

[fkling]

See #235 for a discussion about destructuring.

[jeffmo]

As @fkling points out, ({a: string, b: string})=>{...} actually means you wish for the arrow function to take an object with keys a and b and alias them both to a local binding named string. This is a somewhat unfortunate aspect of the JS grammar that we can't really overwrite.

That said, I can't think of a reason why you shouldn't be able to at least annotate the full destructuring pattern:

(it seems Flow currently doesn't parse this)

type funcArg = {a: string, b: string};
var myfunction = ({a, b}:funcArg) => { ... }

@gabelevi Can you think of any reasons why that ^ shouldn't work as a workaround?

[volkanunsal]

The workaround seems to work fine now.

[adnelson]

The workaround doesn't allow you to specify default arguments in your parameter declaration :(