Add "picks" to include certain key/value pairs from an object

[Siilwyn]

Add "picks" to include certain key/value pairs from an object

[davidchambers]

Such a function could be used to filter a string map by keys, or to create one record from another.

Modern JavaScript syntax suffices if the keys or field names are static:

> (({b, d}) => ({b, d})) ({a: 1, b: 2, c: 3, d: 4})
{b: 2, d: 4}

> (({x, y}) => ({x, y})) ({x: 0, y: 0, color: '#000'})
{x: 0, y: 0}

I prefer ({x, y}) => ({x, y}) to picks (['x', 'y']) because picks is difficult to describe in a Hindley–Milner type system (one must resort to an approximation such as Array String -> a -> b or Array String -> Object -> Object).

What do you think, @Siilwyn? Do you often find yourself filtering string maps by dynamic keys?

[Siilwyn]

In most cases I'm filtering by static keys, I indeed often go with ({x, y}) => ({x, y}) however don't find it that nice to work with when the amount of keys and their length is long. In that case it often go multiline like:

({
  x,
  y,
  someLongKey,
}) =>
({
  x,
  y,
  someLongkey,
})

Which I don't find very readable and means if I change one of the keys I need to do it in two places.

If this method were to make it into Sanctuary, I would say it's mostly useful for big objects of which the values differ in type so having it only on string maps does sound less useful.

[davidchambers]

Thank you for the proposal, @Siilwyn. Currently I do not think the proposed function belongs in the library.