feat: add flip function

[aleclarson]

Tip

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Description

The flip function takes a function and swaps its two arguments. It's most helpful for reversing the order of a comparator (i.e. going from ascending order to descending, or vice versa).

Checklist

• Changes are covered by tests if behavior has been changed or added
• Tests have 100% coverage
• If code changes were made, the documentation (in the /docs directory) has been updated

Resolves

[localusercamp]

Is there any way to make it work with any number of parameters?

[aleclarson]

Is there any way to make it work with any number of parameters?

If we can keep it performant for the two-argument case, I'd say sure.

Maybe something like this?

export function flip(fn, length = fn.length) {
  return length === 2
    ? (a: any, b: any) => fn(b, a)
    : length !== fn.length
      ? (...args: any[]) =>
          fn(...args.slice(0, length).reverse(), ...args.slice(length))
      : (...args: any[]) => fn(...args.reverse())
}

Note: The length property of a function is 0 when only rest arguments are used.

[aleclarson]

Perhaps it might be best to keep it simple (only two arguments) until the demand for more complex use cases is certain.

[aleclarson]

Keeping it just the first two arguments, to align with Ramda (see here)

[github-actions]

A new beta version 12.2.0-beta.c59abfd has been published to NPM. 🚀

To install:

pnpm add radashi@12.2.0-beta.c59abfd

The radashi@beta tag also includes this PR.