Hi Chris, To me the conclusion is exactly the opposite: since we have is_struct/2, there is no need to add a bunch of guards to Kernel. Furthermore, adding such guards to Kernel will only feel natural for Elixir built-types. For everyone else, the usage is more bureaucratic (i.e. import/require a module and then use it). So is_struct/2 is more consistent.
The argument that the Regex struct is an implementation detail does not hold because, given that Elixir has limited built-in types, it has to be a struct by definition. For example, if anyone has ever implemented a protocol for Regex, you are relying on the fact it is a struct - as there is literally no other option. The MapSet is really an issue with Dialyzer not having a mechanism for us to express the constructs we have in Elixir. As mentioned in the linked issue, it manifests in other occasions too, and I would rather fix Dialyzer. Furthermore, a "is_mapset" guard would have the same warnings as is_struct/2", if any, so it wouldn't really address this problem. In any case, Regex.regex? does send mixed signals now that we have is_struct/2, so I will schedule it for deprecation in the long run. Thanks! On Mon, Aug 17, 2020 at 2:08 AM Christopher Keele <christheke...@gmail.com> wrote: > With is_struct/2 coming in 1.11, I think it makes sense to add a guard for > regexes at the same time. > > It is rarely appropriate for Elixir developers to destructure a Regex > struct: its implementation is semi-opaque (partially evidenced by the fact > that it carries a version number > <https://github.com/elixir-lang/elixir/blob/1145dc01680aab7094f8a6dbd38b65185e14adb4/lib/elixir/lib/regex.ex#L146-L148> > with it). The main exception is trying to pattern match on function > parameters to determine if input is a regex versus something else. > > MapSet is another example of a stdlib struct whose implementation is > versioned > <https://github.com/elixir-lang/elixir/blob/1145dc01680aab7094f8a6dbd38b65185e14adb4/lib/elixir/lib/map_set.ex#L57-L61>, > and might make more sense to have a guard for rather than expecting > developers to pattern match it for typecheck guards. However, since it is > fully opaque, there are other problems implementing a guard for them, as > discussed here already: > https://groups.google.com/g/elixir-lang-core/c/2KnRcKTZvuE/m/229Nfw0oCwAJ > > The fact that a Regex is a struct is much more of an implementation detail > than some other, raw-data stdlib structs; like Range, Date, Version, and > URI. An is_regex/1 would help make that clearer, and prevent code like > this > <https://github.com/boydm/phoenix_markdown/blob/ef7b5f76f339babec688021080a70708d9ddf1c1/lib/phoenix_markdown/engine.ex#L80-L88> > that > has to choose between not using guards, or reaching into the struct > implementation detail. > > considerations: > > - we'd want to re-implement Regex.regex?/1 in terms of it and possibly > put that function into a deprecation path. > - we'd need to remove it as an example in the guard Naming > Convention > <https://hexdocs.pm/elixir/naming-conventions.html#is_-prefix-is_foo> > guide. > - could be implemented in either Regex or Kernel. adding to Kernel > sucks, but I think it would be a stronger commitment to the Regex struct > implementation being an opaque detail. > - it would make Regexs feel a lot more first-class Elixir > data-typey, which they already do a lot just by virtue of inspecting as > their sigil constructors. > > -- > You received this message because you are subscribed to the Google Groups > "elixir-lang-core" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to elixir-lang-core+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/elixir-lang-core/071f08ea-f4cf-483e-bfe6-29d98af4bef7n%40googlegroups.com > <https://groups.google.com/d/msgid/elixir-lang-core/071f08ea-f4cf-483e-bfe6-29d98af4bef7n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "elixir-lang-core" group. To unsubscribe from this group and stop receiving emails from it, send an email to elixir-lang-core+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4%2BkHtDY3Uhdr9s6%2BtW_inE-N4QOS0nDzmwk5gq-YyeGvA%40mail.gmail.com.
