[Proposal] Converting @type/@spec to contract/asserts at compile time?

[gasp...@gmail.com]

Hi all!

I increasingly find myself writing more or less exactly same logic as in @type/@spec in body of the function to check incoming arguments.

Would it be helpful if Elixir compiler could wrap function into assert check for incoming arguments and also result generated based on typespec?

I think it would be very useful for

- while running unit tests immediately see where components interaction breaks

- keeping unit tests data in sync while developing - creates more crashes when some stub/test data does not comply with changed logic in function

- running system and checking where it breaks the contracts between components in run-time/while debugging (dyalizer does a great job to extract information during static analysis phase, but runtime can provide more incorrect data :)

- encourage writing more typespecs because benefits of doing so will be visible immediately and not when (occasionally) dyalizer will be run. So make it type specification first class citizen that is not just for documenting code, but also to enforce constraints.

I personally would also love to have possibility for extended typespec that would allow also specify relation between arguments too. Like assert(arg1 + arg2 > 0).

It seems that it may be achieved mostly by rewriting def/defp macros and embedding asserts code generated from @spec around function body.

This will slow down the execution of code and should be compiler option to turn it on/off for production/dev/testing environment separately with on setting in development/testing by default.

What do you think?

/Gaspar

[Louis Pilfold]

Heya

You could write a library that does this rather than modifying Elixir. It would be a cool project :)

Cheers,
Louis

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[gasp...@gmail.com]

On Saturday, September 30, 2017 at 2:36:30 PM UTC+3, Louis Pilfold wrote:

Heya

You could write a library that does this rather than modifying Elixir. It would be a cool project :)

Cheers,
Louis

I wonder if I can redefine  'def' macro and inject it into every module without modifying module to have 'use Something' in them.

/Gaspar

[José Valim]

No, they have to "use something". Being unable to have a magic command that modifies all modules globally is what helps meta-programming in Elixir be a bit sane.

José Valim

www.plataformatec.com.br

Founder and 

Director of R&D

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[Ben Wilson]

No, there is intentionally no way to globally apply a macro.

[gasp...@gmail.com]

On Saturday, September 30, 2017 at 2:46:04 PM UTC+3, José Valim wrote:

No, they have to "use something". Being unable to have a magic command that modifies all modules globally is what helps meta-programming in Elixir be a bit sane.

Okay, then small shell (or perl :) script will do it :) :P

 

[gasp...@gmail.com]

Hi Jose!

Ok, just to speed up my development - where in Elixir source tree can I find type/spec parser? Because it definitely parses them and compains about callbacks signature mismatch :)

/Gaspar

On Saturday, September 30, 2017 at 2:46:04 PM UTC+3, José Valim wrote:

[Shunsuke Kirino]

Hi Gasper,

You might be interested in `defun` macro provided by croma:

https://github.com/skirino/croma/

Hope this helps!

Shunsuke Kirino

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