In my post comparing JSON Path and JSON Pointer, I made the following claim:
A JSON Pointer can be expressed as a JSON Path only when all of its segments are non-numeric keys.
Thinking about this a bit more in the context of the upcoming JSON Path specification, I realized that this only considers JSON Path segments that have one selector. If we allow for multiple selectors, and the specification does, then we can write /foo/2/bar as:
$.foo[2,'2'].bar
Why this works
The /2 segment in the JSON Pointer says
- If the value is an array, choose the item at index 2.
- If the value is an object, choose the value under property “2”.
So to write this as a path, we just need to consider both of these options.
- If the value is an array, we need a
[2]to select the item at index 2. - If the value is an object, we need a
["2"]to select the value under property “2”.
Since the value cannot be both an array and an object, having both of these selectors in a segment [2,"2"] is guaranteed not to cause duplicate selection, and we’re still guaranteed to get a single value.
Caveat
While this path is guaranteed to yield a single value, it’s still not considered a “Singular Path” according to the syntax definition in the specification.
I raised this to the team, and we ended up adding a note to clarify.
Summary
A thing that I previously considered impossible turned out to be possible.
I’ve added a note to the original post summarizing this as well as linking here.
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