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hombre_fatal • 12/08/2024 • 3 replies • view on HN

Like YAML, it's only better in the simple case where everything is top-level and there's only one level of nesting.

Once you want to have arrays of nested objects or objects with arrays, I immediately wish I was just reading JSON so I knew where I was in the tree.

And for that reason, I don't think it's a full contender. I want an answer for the hard cases like nested data, not just another way to write the simple cases which is what TOML is.

For example,

    [[a.b]]
    x = 1

    [a]
    y = 2
Versus:

    {
      "a": {
        "b": [ { "x": 1 } ],
        "y": 2
      }
    }
It's easy to complain that the latter is noisier. But that's nothing compared to being clear.

Replies

zahlman • 12/08/2024

It's not made explicit in the documentation, but TOML is very nearly a superset of JSON - just using `=` to separate key-value pairs instead of `:`, and requiring top-level names to be given explicitly, and requiring the "inline" bits to be on a single line. In TOML, your example can equivalently be:

    a = { b = [ { x = 1 } ], y = 2 }
(And yes, that can be the entire document; you can have an inline table before the first table header.)

Of course, this doesn't help if you want the top level to be an "array" rather than an "object" (in JSON parlance), or if you want the entire document to represent a single primitive value. But these uses are discouraged at best anyway.

But really the goal of TOML is to highlight the location of important parts of the deserialized tree structure (hence the ability to use arbitrary long dotted paths in table headers) rather than the structure itself. It's IMO a beautiful implementation of the idea "flat is better than nested" from the Zen of Python, and it neatly sidesteps an issue I asked about many years ago on Stack Overflow (https://stackoverflow.com/questions/4372229 - the question was rightfully closed, as this sort of discussion doesn't fit the Q&A format; but it made sense to ask at the time).

I don't know if a direct comparison of TOML to YAML is fair. Among other differences, the standard way to parse YAML in Python involves a third-party library that brings in a ~2.5 MB compiled C library. Every TOML implementation I encountered - including the one that made it into the standard library - is pure Python.

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arp242 • 12/09/2024

Your TOML is rather convoluted, a more normal way to write it would be:

  [a]
  b = [{x = 1}]
  y = 2
Or alternatively:

  a.b = [{x = 1}]
  a.y = 2
Some parsers allow newlines in TOML inline tables, so you can do:

  a = {
    b = [{x = 1}],
    y = 2,
  }
That's supposed to be in the next TOML standard, but that seems indefinitely stalled as the (only) maintainer has seemingly lost interest and there hasn't been any movement for a long time.
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okanat • 12/08/2024

This is also the reason I prefer XML to JSON when things really got complex. XML is verbose but it is very readable on long form. I wish Rust actually used JSON or XML as Cargo file format.

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