Re: Metadata loss. What am I doing wrong?

[Andrey Antukh]

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 :

> 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  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- :
>>
>>> 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
>>> 
>>>  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 -  / <
 ni...@niwi.be>
 http://www.niwi.be 
 https://github.com/niwibe

>>>
>>
>>
>> --
>> Andrey Antukh - Андрей Антух -  / <
>> n...@niwi.be>
>> http://www.niwi.be 
>> https://github.com/niwibe
>>
>> --
>> You received this message because you are subscribed to the Google
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>


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http://www.niwi.be 
https://github.com/niwibe

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Re: Metadata loss. What am I doing wrong?

[Mike Rodriguez]

In reference to [1]:

I do feel like the metadata loss on many macros is undesirable though and I 
wish it were addressed. It certainly  feels "unhygienic", just in a new sense 
of the term. 

[1] https://github.com/jonase/eastwood#unused-meta-on-macro

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Re: Metadata loss. What am I doing wrong?

[Mike Rodriguez]

+1 to Eastwood. It is great. 

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Re: Metadata loss. What am I doing wrong?

[Andy Fingerhut]

The Eastwood [1] Clojure lint tool has a few warnings in it that warn about
unused metadata in your code.

The :unused-meta-on-macro warns about metadata on macro invocations, which
is usually ignored by Clojure [2].

The :wrong-tag warns about unused type tag metadata on Vars, and
non-fully-qualified Java class names on arg vectors [3].

Andy

[1] https://github.com/jonase/eastwood
[2] https://github.com/jonase/eastwood#unused-meta-on-macro
[3] https://github.com/jonase/eastwood#wrong-tag

On Tue, May 5, 2015 at 5:51 PM, Mike Rodriguez  wrote:

>
> What you wanted here was
>
>  (meta '^:abc some-symbol)
>
> It's a little weird but the reader attaches the metadata to the symbol.
> Then the quote just evaluates directly to the same symbol, so the metadata
> is preserved.
>
> I agree that metadata can be confusing though. Especially around where AND
> HOW you put the metadata for a functions return value(s).
>
> See [1] for more on that confusing track...
>
> Also there are plenty of subtle "gotchas" to macros etc that do not
> preserve metadata. 'clojure.core/or' is a good example of that.
>
> A search for "Clojure preserve metadata" will likely turn up a good list
> of Jiras out there to fix areas that do not preserve metadata as expected.
>
> Looks like there are some tips at [2].
>
> [1] http://dev.clojure.org/jira/browse/CLJ-1232
> [2]
> http://stackoverflow.com/questions/4673011/what-functions-in-clojure-core-preserve-meta
>
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Re: Metadata loss. What am I doing wrong?

[Mike Rodriguez]

What you wanted here was 

 (meta '^:abc some-symbol)

It's a little weird but the reader attaches the metadata to the symbol. Then 
the quote just evaluates directly to the same symbol, so the metadata is 
preserved. 

I agree that metadata can be confusing though. Especially around where AND HOW 
you put the metadata for a functions return value(s).   
 
See [1] for more on that confusing track...

Also there are plenty of subtle "gotchas" to macros etc that do not preserve 
metadata. 'clojure.core/or' is a good example of that. 

A search for "Clojure preserve metadata" will likely turn up a good list of 
Jiras out there to fix areas that do not preserve metadata as expected. 

Looks like there are some tips at [2]. 

[1] http://dev.clojure.org/jira/browse/CLJ-1232
[2] 
http://stackoverflow.com/questions/4673011/what-functions-in-clojure-core-preserve-meta

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Re: Metadata loss. What am I doing wrong?

['wparke...@yahoo.com' via Clojure]

>From your comments, I suspect this may be a source of confusion as well:

When you have something like (defn ^{:doc "Increments"} a-fn [x] (+ x 1)) 
the metadata is attached to the symbol at read time.  However, during the 
compilation process, the metadata on the symbol is transferred to the Var 
that holds the function created.  If you want to access this metadata you 
have to access the Var itself, not the function.

user=> (meta a-fn)
nil
user=> (meta #'a-fn)
{:ns #, :name a-fn, :file "NO_SOURCE_PATH", :column 1, 
:line 1, :arglists ([x]), :doc "Increments"}

The #' syntax is shorthand for accessing the Var.  You can see this process 
in the following code:

(let [fn-def-sym (with-meta 'b-fn {:here true})
  fn-def-code `(defn ~fn-def-sym [x#] (+ x# 1))]
  (eval fn-def-code))

#'user/b-fn
user=> (b-fn 2)
3
user=> (meta b-fn)
nil
user=> (meta #'b-fn)
{:ns #, :name b-fn, :file "NO_SOURCE_PATH", :here true, 
:column 1, :line 1, :arglists ([x__769__auto__])}

The important thing here is that the definition code is manually built up 
using a symbol that has metadata given manually, which is then transferred 
to a Var when the code is evaluated.





On Tuesday, May 5, 2015 at 1:31:40 PM UTC-5, 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 - > / <
> ni...@niwi.be >
> http://www.niwi.be 
> https://github.com/niwibe
>  

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Re: Metadata loss. What am I doing wrong?

[adrian . medina]

Because ' is a reader macro which expands to the list (quote some-symbol), 
so the metadata is applied to the list, and not the symbol. You can verify 
this in the REPL - (meta (quote ^:abc 'some-symbol))

On Tuesday, May 5, 2015 at 5:43:19 PM UTC-4, Andy- wrote:
>
> Frankly, I would've (meta ^:abc 'some-symbol) expected to work. Maybe 
> somebody else can weigh in on why this one is a no-go.
>
> On Tuesday, May 5, 2015 at 5:01:19 PM UTC-4, Andrey Antukh 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- :
>>
>>> 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 
>>> 
>>>  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 -  / <
 ni...@niwi.be>
 http://www.niwi.be 
 https://github.com/niwibe
  
>>>
>>
>>
>> -- 
>> Andrey Antukh - Андрей Антух -  / > >
>> http://www.niwi.be 
>> https://github.com/niwibe
>>  
>

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Re: Metadata loss. What am I doing wrong?

[James Reeves]

I expect because 'some-symbol is shorthand for (quote some-symbol), so
you're attaching the metadata to a list that disappears once it's evaluated.

- James

On 5 May 2015 at 22:43, Andy-  wrote:

> Frankly, I would've (meta ^:abc 'some-symbol) expected to work. Maybe
> somebody else can weigh in on why this one is a no-go.
>
> On Tuesday, May 5, 2015 at 5:01:19 PM UTC-4, Andrey Antukh 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- :
>>
>>> 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
>>> 
>>>  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 -  / <
 ni...@niwi.be>
 http://www.niwi.be 
 https://github.com/niwibe

>>>
>>
>>
>> --
>> Andrey Antukh - Андрей Антух -  / > >
>> http://www.niwi.be 
>> https://github.com/niwibe
>>
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Re: Metadata loss. What am I doing wrong?

[Andy-]

Frankly, I would've (meta ^:abc 'some-symbol) expected to work. Maybe 
somebody else can weigh in on why this one is a no-go.

On Tuesday, May 5, 2015 at 5:01:19 PM UTC-4, Andrey Antukh 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- >:
>
>> 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 
>> 
>>  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 -  / <
>>> ni...@niwi.be>
>>> http://www.niwi.be 
>>> https://github.com/niwibe
>>>  
>>
>
>
> -- 
> Andrey Antukh - Андрей Антух - > / <
> ni...@niwi.be >
> http://www.niwi.be 
> https://github.com/niwibe
>  

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Re: Metadata loss. What am I doing wrong?

[James Reeves]

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  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- :
>
>> 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
>> 
>>  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 -  / <
>>> ni...@niwi.be>
>>> http://www.niwi.be 
>>> https://github.com/niwibe
>>>
>>
>
>
> --
> Andrey Antukh - Андрей Антух -  / <
> n...@niwi.be>
> http://www.niwi.be 
> https://github.com/niwibe
>
> --
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Re: Metadata loss. What am I doing wrong?

[Andrey Antukh]

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- :

> 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
> 
>  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 -  / > >
>> http://www.niwi.be 
>> https://github.com/niwibe
>>
>


-- 
Andrey Antukh - Андрей Антух -  / 
http://www.niwi.be 
https://github.com/niwibe

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Re: Metadata loss. What am I doing wrong?

[Andy-]

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 
 
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 - > / <
> ni...@niwi.be >
> http://www.niwi.be 
> https://github.com/niwibe
>  

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Re: Metadata loss. What am I doing wrong?

[James Reeves]

When dealing with metadata, it's important to understand the difference
between these two expressions:

^{:foo :bar} baz

(with-meta baz {:foo :bar})

The first expression attaches metadata to the 'baz' symbol at compile time.
The second expression attaches metadata to the data held in 'baz' at
runtime.

The ^ syntax is essentially used for passing information to the Clojure
compiler, and to macros. It's not runtime information.

- James

On 5 May 2015 at 19:31, 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 -  / <
> n...@niwi.be>
> http://www.niwi.be 
> https://github.com/niwibe
>
> --
> You received this message because you are subscribed to the Google
> Groups "Clojure" group.
> To post to this group, send email to clojure@googlegroups.com
> Note that posts from new members are moderated - please be patient with
> your first post.
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Metadata loss. What am I doing wrong?

[Andrey Antukh]

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 -  / 
http://www.niwi.be 
https://github.com/niwibe

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