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Comments inline
On 08/15/2014 06:47 AM, Dave Tenny wrote:
> This is getting old. Any suggestions or plans to fix it? Do I need to use
> some other common
declaration style for functions?
>
> ; CIDER 0.5.0 (Clojure 1.6.0, nREPL 0.2.3)
> user> (defn foo [& {:keys [bar]}] bar)
> #'user/foo
> user> (foo :baz 1)
> nil
>
> In my opinion the compilation of the call to foo should have
complained about :baz not matching a known parameter.
At the implementation level, there is no "formal parameter" here. You've
defined a variadic function, who's varargs are to be treated as a map
key/value sequence, and the key ":bar" of which you wish to extract and
bind to a local. "bar" here is _not_ a formal parameter of foo, it's
simply a local destructured from the map converted varargs.
> Failure to do this leads to lots of extra debugging because someone had a
> typo in a keyword name,
> e.g. ":Name" instead of ":name" or :product instead of :project, or
whatever.
>
> This is probably the leading cause of unexpected program operation in
clojure for me.
For a number of implementation reasons, this is not something that
clojure/core is ever likely to provide better support for. Prismatic's
Schema, core.typed and aggressive use of preconditions are the best
tools available for you to guard against these errors. For exactly this
reason I have personally adopted the practice of asserting what equates
to a full typecheck of all arguments in function preconditions.
Clojure/core doesn't do this in the name of "performance", but for user
code it's easy enough to remove typechecks if the overhead becomes
significant.
Reid
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