Thank you very much to all!
Now I completely understand the metadata behavior with the reader. I'll try
to adopt eastwood, thanks for the suggestion.
Is clearly that the documentation confuses a little bit.
Cheers!
Andrey
2015-05-05 23:25 GMT+02:00 James Reeves <ja...@booleanknot.com>:
> The documentation is rather misleading, as it implies that "obj" can be a
> symbol. However, because ^ is a reader macro, it is applied to "obj" before
> it is evaluated.
>
> Clojure maps, vectors and sets all evaluate to themselves, so attaching
> metadata to the unevaluated expression via the ^ reader macro, is the same
> as attaching it to the evaluated expression via with-meta.
>
> So:
>
> ^:abc foo
> ^:abc [1 2 3]
>
> Will both attach the metadata directly to the literal value following it,
> but because 'foo' evaluates to something else, the reader metadata is lost
> after the symbol is evaluated.
>
> - James
>
> On 5 May 2015 at 22:01, Andrey Antukh <n...@niwi.be> wrote:
>
>> Thanks to both for the responses, but I stil not clearly understand.
>>
>> The documentation says very clearly that:
>>
>> In addition to with-meta, there are a number of reader macros (The
>> Reader: Macro Characters) for applying metadata to the expression following
>> it:
>> ^{:doc "How obj works!"} obj - Sets the metadata of obj to the provided
>> map.
>> Equivalent to (with-meta obj {:doc "How obj works!"})
>>
>>
>> (def foo ^:abc [1 2 3]) -> (meta foo) -> {:abc true}
>> (def foo ^:abc some-func) -> (meta foo) -> nil
>> (def foo ^:abc 'some-symbol) -> (meta foo) -> nil (In clojure
>> programming book uses example attaching metadata using the reader to the
>> symbol, but seems it not works as expected)
>>
>> Is a little bit confusing. The metadata documentation says clearly that
>> are equivalent, but are not equivalent.
>>
>>
>> Thank you very much again.
>>
>> Regards.
>> Andrey
>>
>> 2015-05-05 21:49 GMT+02:00 Andy- <andre.r...@gmail.com>:
>>
>>> In addition to James comment: IMO clojure.org/metadata should be
>>> clearer about this. It's mentioned more clearly on the reader page:
>>> http://clojure.org/reader#The%20Reader--Macro%20characters
>>> "The metadata reader macro first reads the metadata and attaches it to
>>> the next form read (see with-meta
>>> <http://clojure.github.io/clojure/clojure.core-api.html#clojure.core/with-meta>
>>> to
>>> attach meta to an object):"
>>>
>>> Stress on *next form read*.
>>>
>>> On Tuesday, May 5, 2015 at 2:31:40 PM UTC-4, Andrey Antukh wrote:
>>>>
>>>> Hi!
>>>>
>>>> I have some trouble with clojure metadata / reader and I do not know if
>>>> I'm doing something wrong.
>>>>
>>>> I have this code:
>>>>
>>>> (defn some-func [])
>>>>
>>>> (def func ^:abc some-func)
>>>>
>>>> (assert (= (meta func) {:abc true}))
>>>>
>>>> (def data [[:bar (with-meta some-func {:abc true})]
>>>> [:baz ^:abc some-func]])
>>>>
>>>> (assert (= (meta (get-in data [0 1])) {:abc true}))
>>>> (assert (= (meta (get-in data [1 1])) {:abc true}))
>>>>
>>>> It fails in the first assert and in the last (if I comment the first
>>>> one obviously). I do not understand why that form of metadata does not
>>>> works
>>>> as I expect (http://clojure.org/metadata)
>>>>
>>>> Thank you very much.
>>>>
>>>> Regards.
>>>> Andrey
>>>>
>>>> --
>>>> Andrey Antukh - Андрей Антух - <andrei....@kaleidos.net> / <
>>>> ni...@niwi.be>
>>>> http://www.niwi.be <http://www.niwi.be/page/about/>
>>>> https://github.com/niwibe
>>>>
>>>
>>
>>
>> --
>> Andrey Antukh - Андрей Антух - <andrei.anto...@kaleidos.net> / <
>> n...@niwi.be>
>> http://www.niwi.be <http://www.niwi.be/page/about/>
>> https://github.com/niwibe
>>
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>
--
Andrey Antukh - Андрей Антух - <andrei.anto...@kaleidos.net> / <n...@niwi.be
>
http://www.niwi.be <http://www.niwi.be/page/about/>
https://github.com/niwibe
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