alt Hacker NewsAt that point, you're making all your configuration fields strings and adding another parsing step after the json/toml/yaml parser is done with it. That's not ideal either; either you write a bunch of parsing code (not terribly difficult but not something I wanna do when I can just not), or you use some time library to parse a duration string, in which case the programming language and time library you happen to use suddenly becomes part of your config file specification and you have to exactly re-implement your old time handling library's duration parser if you ever want to switch to a new one or re-implement the tool in another language.
I don't think there are great solutions here. Arguably, units should be supported by the config file format, but existing config file formats don't do that.
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> adding another parsing step after the json/toml/yaml parser is done with it. That's not ideal either
I'd argue that it is ideal, in the sense that it's the sweet spot for a general config file format to limit itself to simple, widely reusable building blocks. Supporting more advanced types can get in the way of this.
Programs need their own validation and/or parsing anyway, since correctness depends on program-specific semantics and usually only a subset of the values of a more simply expressed type is valid. That same logic applies across inputs: config may come from files, CLI args, legacy formats, or databases, often in different shapes. A single normalization and validation path simplifies this.
General formats must also work across many languages with different type systems. More complex types introduce more possible representations and therefore trade-offs. Even if a file parser implements them correctly (and consistently with other such parsers), it must choose an internal form that may not match what a program needs, forcing extra, less standard transformation and adding complexity on both sides for little gain.
Because acceptable values are defined by the program, not the file, a general format cannot fully specify them and shouldn’t try. Its role is to be a medium and provide simple, human-usable (for textual formats), widely supported types, avoid forcing unnecessary choices, and get out of the way.
All in all, I think it can be more appropriate for a program to pick a parsing library for a more complex type, than to add one consistently to all parsers of a given file format.
Another parsing step is the common case. Few parameters represent untyped strings where all characters and values are valid. For numbers as well, you often have a limited admissible range that you have to validate for. In the present case, you wouldn’t allow negative numbers, and maybe wouldn’t allow fractional numbers. Checking for a valid number isn’t inherently different from checking for a regex match. A number plus unit suffix is a straightforward regex.
TOML has a datetime type (both with or without tz), as well as plain date and plain time:
We should extend it with durations: And like for datetimes, we should have a readable variant: Edit: discussed in detail here: https://github.com/toml-lang/toml/issues/514