如何在不更新对函数的所有调用的情况下向纯函数添加新参数？

Question

I make a pure function (example in js, but the question doesn't depend on the language) with one input argument and call it all over my application.

var day = 'Tuesday';
var doYouExist = function(you) {
    return !!you;
}

Then I realise that I should only check if you exist on Tuesdays so I decide to update the function...

var day = 'Tuesday';
var doYouExist = function(you) {
    if (day === 'Tuesday') {
      return !!you;
    }
}

But now it's not pure. I could add day as an argument, but the day variable isn't available in all of the places doYouExist() is called.

So my choices are either:

1. Use an impure function
2. Inject 'day' to all of the places the function is called, then update the function and every call to that function to include a second argument.

Until now I've been using choice 1, but I don't know the recommended pattern (or any way to actually achieve what I want) for a functional approach.

Answer 1

如果day是一个常数，则您无需执行任何操作，因为您的函数仍然是纯函数。