[ANN] Clojure 1.9.0-alpha12

[Alex Miller]

Clojure 1.9.0-alpha12 is now available.

Try it via

- Download: https://repo1.maven.org/maven2/org/clojure/clojure/1.9.0-alpha12

- Leiningen: [org.clojure/clojure "1.9.0-alpha12"]

1.9.0-alpha12 includes the following changes since 1.9.0-alpha11:

- spec performance has been improved for many use cases

- spec explain printer is now pluggable via the dynamic var clojure.spec/*explain-out*

  which should be a function that takes an explain-data and prints to *out*

- when a macro spec fails during macroexpand, throw ex-info with explain-data payload

  rather than IllegalArgumentException

- pprint prints maps with namespace literal syntax when *print-namespace-maps* is true

- CLJ-1988 - coll-of, every extended to conform sequences properly

- CLJ-2004 - multi-spec form was missing retag

- CLJ-2006 - fix old function name in docstring

- CLJ-2008 - omit macros from checkable-syms

- CLJ-2012 - fix ns spec on gen-class signatures to allow class names

- CLJ-1224 - record instances now cache hasheq and hashCode like maps

- CLJ-1673 - clojure.repl/dir-fn now works on namespace aliases

[lvh]

CLJ-1224 appears to have broken Datascript, which now doesn’t compile:

Exception in thread "main" java.lang.AssertionError: The names in #{__hash __meta __hasheq __extmap} cannot be used as field names for types or records., compiling:(datascript/db.cljc:369:1)

The ticket mentions CLJS compat; it looks like it only adds __hash in CLJ:

https://github.com/tonsky/datascript/blob/0684c4102706bf4ee8b2496ad35c32ced08640fc/src/datascript/db.cljc

Not sure what the ideal way to solve this is…

lvh

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[Alex Miller]

I've commented on this in multiple other places but for the sake of completeness...

Datascript is extending some defrecords to the IHashEq protocol to add custom hash caching. In particular, this extension is adding custom fields __hash and __hasheq, which happen to be the (obvious) names of the new fields added in alpha12 via CLJ-1224 to support built-in hashcode caching (like maps). 

Records are designed to hash like maps and to have hashing provided by the language, not customized by the user. Due to this, and to the use of fields with __-prefix, I consider the existing Datascript code to be invalid. I have examined all uses of __hash fields and IHashEq on Github (many many pages of results) and have found no other examples of this in tandem with defrecord.

Note that deftype does NOT provide a hashing mechanism - deftypes are not given map capabilities, hashing, or many of the things provided automatically by defrecord. It is thus common, acceptable, and encouraged for deftype users to provide a hashing strategy appropriate to the deftype. My comments above apply only to defrecord, not to deftype.

Datascript should either remove these extensions or switch to using deftype for these use cases.

[lvh]

Thanks for investigating this in-depth, Alex! Very much appreciated :) Sorry about filing the issue in several places; I genuinely wasn’t sure where the problem was :)

[Alex Miller]

Regarding performance, the validation benchmark project has been updated with alpha12:

http://muhuk.github.io/validation-benchmark

[Rangel Spasov]

Hey guys, 

I'm getting this compilation error with Alpha 12 (use the gist link)

https://gist.github.com/raspasov/188a8e60f1f6e695b6492cf2d3d19471

Rangel

[Alex Miller]

The keys of an :or destructuring map should be symbols, not keywords.

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[Rangel Spasov]

Ah, got it - https://github.com/ztellman/aleph/commit/7d6f2f5bf743301c5a4ab0705725bf9b50b91896 - thanks!

[Alex Miller]

Oh yeah, I fixed that one a while back. :)  I think there is a newer release of aleph with the change.

[Rangel Spasov]

Yup- upgraded to [aleph "0.4.2-alpha8"] and it's fixed - thanks again!