Feature request - Make a parameter required for callback function

[ORESoftware]

This video shows the problem:

https://www.useloom.com/share/1a0f1e84083049ff8f745a3a1f17ac03

basically I have this

v.run =  t => { return t.foo()};

run(() => {   
    //  this compiles
});

run(t => {   
    //  but I want to make the t parameter required!
});

the "plain" function satisfies the typings, but I want to make the parameter required, not optional. I can't really explain but it should be clear from the (rambling) video. Thanks.

[mhegazy]

have no parameters is semantically equivalent to having a parameter and ignoring its value at runtime. the later is not an indication of invalid code, and so is the earlier. a canonical example here is map.. most users never specify the second or third arguments. the caller has to always provide them just the same.

[ORESoftware]

Totally disagree on this one.

Array.prototype.map = (x: Function, y?: thisArg)

it does not look like this:

Array.prototype.map = (x?: Function, y?: thisArg)

if you don't pass the first argument, you are f*cked, because a TypeError is coming your way.

it is VERY important to tell the user that the first argument is required. Omitting an argument is a failure at runtime!!

So with that said, I need to tell my users that this ok

run(function(t){

});

but that this is not ok:

run(function(){

});

how do I do that?

[mhegazy]

run(function(t){
   // forget to use t
});

and

run(function(){

});

are identification.. so you can tell them to make sure to use the argument in the docs i guess..

[gcnew]

It would be more helpful if you post a snippet displaying the issue. The way I see it, the only code that needs such behaviour are functions that inspect function.length or do toString() hacks. Honestly, both of these are questionable practices.

[ORESoftware]

@gcnew if you use

[].map()

you are going to get a TypeError because you failed to pass it a function

same with my code (I just improved the example)

if you fail to pass t, then you will get a TypeError because t.foo() will get called, and t will be undefined.

@mhegazy yes I suppose a linting tool / rule could be used to enforce that the parameter is there. I am not sure how to classify this and it's a bit confusing tho.

[ORESoftware]

Ultimately this is the difference between arguments and parameters?

// here are arguments
t.foo(a,b,c);      // a,b,c are arguments

// here are parameters
t.foo = function(a,b,c){   // a, b, c are parameters

};

at least that's the nomenclature that I currently adhere to lol

so I want to make parameters to be forced to be in place

what I want is useful for APIs, not for library code

the user is essentially implementing foo, but I need to tell them that foo needs to take at least one parameter

[RyanCavanaugh]

It's in the FAQ and this has been covered many many times before. See #17868 for a recent recitation of this debate.

[ORESoftware]

@RyanCavanaugh re: https://github.com/Microsoft/TypeScript/wiki/FAQ#why-are-functions-with-fewer-parameters-assignable-to-functions-that-take-more-parameters

I'd like see some option we can use to make functions with fewer parameters not assignable to functions that take more parameters

is that possible? A flag in tsconfig.json? dunno

[ORESoftware]

So it's working here:

so I wonder why in my example it wasn't working? dunno