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https://issues.apache.org/jira/browse/THRIFT-428?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12695955#action_12695955
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Chad Walters commented on THRIFT-428:
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Bryan, does the Ruby implementation now support a reasonable hash function for
structs?
It's interesting how the importance of smooth interoperability across languages
and the importance of flexibility for languages to be independent of the
constraints imposed by other languages change places when different use cases
and language sets are affected (see discussion in THRIFT-395).
Since there clearly isn't consensus here and we are close to the 0.1 release, I
will defer this. If someone wants to implement David's suggestion of a compiler
flag to select the behavior, I wouldn't complain.
I will probably keep raising this issue until the community and/or the PMC come
up with better guidelines around interoperability vs. flexibility that don't
change based on convenience for any particular set of use cases and language
choices but rather provide a principled basis for decision-making.
> Restrict map keys to integers and strings only
> ----------------------------------------------
>
> Key: THRIFT-428
> URL: https://issues.apache.org/jira/browse/THRIFT-428
> Project: Thrift
> Issue Type: Improvement
> Components: Compiler (General)
> Affects Versions: 0.1
> Reporter: Chad Walters
> Fix For: 0.2
>
>
> For the sake of better interoperability, particularly with PHP, it would be a
> good idea to restrict map keys to be only of integer and string type.
> Handling of structures and containers as key types is a pretty mixed bag
> across the main supported languages. The current state of affairs is:
> C++: Containers with containers as keys (with no structs involved) are fine.
> If a struct (or container of structs, or container of containers of structs,
> etc.) is to be used as a map key, it must have a comparison (less than)
> operator defined.
> Java: Containers and structs can be used as map keys or set elements. It is
> not entirely safe, but this is the Java convention (trust the application
> developer). structs cannot be used in sorted containers. Using structs as
> map keys without an optional dependency (apache commons lang) is very
> inefficient because structures all have a hashCode of 0 without it. (Can
> binaries be used as keys?)
> Python: Using mutable containers as map keys is impossible. Using mutable
> structures as map keys is possible, but unsafe and goes against a very strong
> Python convention. We are pretty close to having implementations of
> immutable containers and structures, but the code will probably end up being
> pretty bulky or pretty skeevy.
> Ruby: (Maybe someone can fill in more details?) Structures as map keys are
> very inefficient because all structures have a hash code of zero.
> PHP: Using structures or containers as map keys (or set elements) in PHP is
> currently impossible, and might be impossible to implement. Only strings and
> numbers can be associative array keys in PHP.
> Erlang: Any struct or container can be a map key or set element. There are
> no safety or performance issues. Erlang is pretty cool like that.
> I'd like us to consider doing this for 0.1 so it's in there for the first
> official Apache release.
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