Consider implementing ES6 compact-style multi-select-hash like {x, y}

[springcomp]

Compact syntax for multi-select-hash

JEP	14
Author	Dan Vanderkam, Maxime Labelle
Status	draft
Created	26-Feb-2022

Abstract

This JEP proposes a grammar modification to support ES6-style compact multi-select-hash constructs.

Motivation

Consider the following JSON document:

{
  "values": [
    {"id": 1, "first": "Bill", "last": "Gates"},
    {"id": 2, "first": "Larry", "last": "Page"}
  ]
}

Let’s say we wanted to return a hash containing ids and first names.
This is currently possible using the following syntax:

values[*].{id:id, first:first}

Since {x:x, y:y} is such a common pattern, ES6 introduced compact object literal notation to simplify this. In ES6, {x,y} is equivalent to {x:x, y:y}.

This JEP supports this syntax to make JMESPath usage slightly less verbose.

Specification

What is currently the multi-select-hash production will be renamed
to multi-select-hash-keyval:

multi-select-hash_keval = "{" ( keyval-expr *( "," keyval-expr ) ) "}"

The multi-select-hash production will be modified slightly to accomodate
the syntax changes:

multi-select-hash	= multi-select-hash-key
multi-select-hash	=/ multi-select-hash-keyval

The new multi-select-hash-key production is defined like so:

multi-select-hash-key = "{" ( identifier *( "," identifier ) ) "}" 

Here is the full update to the grammar:

multi-select-hash        = multi-select-hash-key
multi-select-hash        =/ multi-select-hash-keyval

multi-select-hash-key    = "{" ( identifier *( "," identifier ) ) "}" 
multi-select-hash-keyval = "{" ( keyval-expr *( "," keyval-expr ) ) "}"

Motivating Example

With these changes defined, the expression in the “Motivation” section can be
be written as:

values[*].{id, first}

Which evaluates to [{"id": 1, "first": "Bill"}, {"id": 2, "first": "Larry"}].

Rationale

This JEP is inspired by an idea from Dan Vanderkam.

[innovate-invent]

I am concerned this is beginning to conflict with the guiding principle of "one way to do something".

Can anyone suggest what other functionality that syntax could represent that we will be forgoing with this implementation?

I can see {x,y} being a set syntax that results in a list with de-duplicated values (x=1, y=1: {x,y}=>[1]). I would also argue that this example should be implemented as a set() function.