Elixir v1.6 released: code formatter, dynamic supervisors, and more

Re:Elixir v1.6 released: code formatter, dynamic supervisors... by dgllghr on Wednesday January 17, 2018 @02:22PM (#16170879)

It might be a small thing, but I am most excited about @defguard. I find that splitting a function to match on different inputs and using guards creates elegant, clear, and maintainable code, but if a guard statement is too large, that effect is diminished and I fall back to `if` or `case`. @defguard allows me to stick to the more elegant (in my opinion) solution.

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Re:Elixir v1.6 released: code formatter, dynamic supervisors... by davidkuhta on Wednesday January 17, 2018 @02:54PM (#16171186)

For those interested in some of the thought-process of defguard check out Chris Peele's gist of his development process:

https://gist.github.com/christhekeele/76c3e37cb9082274f52f79...

While not the final spec per his PR, a really good look at the internals nonetheless.

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Re:Elixir v1.6 released: code formatter, dynamic supervisors... by christhekeele on Wednesday January 17, 2018 @08:49PM (#16173963)

You can follow my development even further—the lingering question in that gist is how to expand the guard code to see if it is valid in a guard.

I tried my hand at a pure-Elixir guard expansion in an earlier PR, documenting my thoughts as I went: https://github.com/elixir-lang/elixir/pull/5854

After José gave me some direction in response to that, I produced the ultimate PR: https://github.com/elixir-lang/elixir/pull/5857

It simply relies on calling the :elixir_expand.expand function that the compiler uses, with a guard context—so the defguard implementation is always up-to-date with what the compiler allows in guards. Waaay more elegant than munging AST myself.

Funnily enough, the tests I wrote for defguard actually uncovered some missing assertions in that function. Some invalid expressions would make it past that step and return a different error much deeper in. It's kinda cool I indirectly contributed to the compiler.

I took on the feature mostly because over 4 years ago I'd made a gist to do exactly that, minus the validation, and when I found the issue on github for it, it gave me a lot of pleasant closure to get it merged in! https://gist.github.com/christhekeele/8284977/revisions#diff...

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Re:Elixir v1.6 released: code formatter, dynamic supervisors... by qaq on Wednesday January 17, 2018 @09:43PM (#16174223)

+1 very welcome addition for exactly the reasons you have outlined.

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