Branch on values

To shape the output by a value in the input, switch on it. switch reads a branch key with source and selects the matching descriptor from cases:

/entry:
  switch:
    source: /kind
    cases:
      video:
        source: /
        mapping:
          /title: /title
          /minutes: { source: /duration, as: number }
      article:
        source: /
        mapping:
          /title: /title
          /pages: { source: /pageCount, as: number }

With a video record:

{ "kind": "video", "title": "Mapping Live", "duration": "12" }

the output is:

{ "entry": { "title": "Mapping Live", "minutes": 12 } }

With an article record:

{ "kind": "article", "title": "On Mapping", "pageCount": "8" }

the output is:

{ "entry": { "title": "On Mapping", "pages": 8 } }

A case can be any descriptor: a pointer, a nested mapping, or a $ref to a registered mapping. An unmatched key selects nothing and the pairing writes nothing.