Strings are indexed. They are a special case because String is a Java final
class that cannot be "extended" to support the core interfaces inside
Clojure's Java implementation. If Clojure were itself protocol-based (like
ClojureScript is), the protocol could cover this without the special case.
On Thursday, April 21, 2016 at 10:48:18 AM UTC-5, Mars0i wrote:
>
> The docstring for 'get' says nothing explicit about vectors ("Returns the
> value mapped to key, not-found or nil if key not present.") but most of us
> know that vectors can be viewed as associative data structures where
> indexes are like keys:
>
> (get [\a \b \c] 1)
> \b
>
> 'get' also works on strings:
>
> (get "abc" 1)
> \b
>
> However, strings are not treated as vectors or maps in other contexts:
>
> (assoc "abc" 1 \Z)
> ClassCastException java.lang.String cannot be cast to
> clojure.lang.Associative
>
>
Being able to *add* something to an indexed collection is a totally
different "behavior" than looking something up by index. Strings don't do
that part.
> This combination of behaviors is confusing. If strings are vectors, then
> 'assoc' and other similar functions should work with them, and maybe I
> should be able to do this to index into a string:
>
> ("abc" 1)
> ClassCastException java.lang.String cannot be cast to clojure.lang.IFn
>
> If strings are not vectors, then they seem to be a special case for
> 'get'. One might argue that the very terse docstring for 'get' should note
> its use with vectors, but once you understand the sense in which vectors
> are like maps, the of 'get' use with vectors is implicitly covered by what
> the docstring says. However, the use of 'get' with strings is not
> implicitly covered by what the docstring says. If it was, then the last
> two examples I gave should work.
>
> (I'd be willing to file a ticket on this, but the puzzling behavior is not
> new, and I suspect that there's something I'm not understanding.)
>
I think the current behavior and docs are correct and I'm not yet convinced
there is a change needed. (But feel free to keep discussing and maybe I'll
change my mind. :)
Alex
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