Re: Questions regarding Map vs Record and usage
FWIW, I use:
- (->Book "Lord of the Rings", "Tolkien")
- when I define the record instance with the default fields, and the
number of default fields is a small number
- (map->Book {:title "The Fellowship of the Ring",
:author "Tolkien",
:series "The Lord of the Rings",
:publisher "Mariner Books",
:year 2012,
:ISBN-10 "0547928211",
:my-rating 10})
- The explicit key names are good documentation when
- there are many fields in the defrecord, or
- when adding entries not in the defrecord (eg. my-rating)
Greg
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Re: Questions regarding Map vs Record and usage
On 4/9/14, 12:51 PM, Anthony Ortiz wrote:
I see that there are several ways of instantiating a record :
(->Book "Lord of the Rings", "Tolkien")
(Book. "Lord of the Rings", "Tolkien")
#user.Book{:title "Lord of the Rings", :author "Tolkien"}
You missed one:
(map->Book {:title "Lord of the Rings", :author "Tolkien"})
Questions :
1) The second version is referred to as the "original" version so I'm
wondering which is the preferred method.
The helper constructor fns are preferred and not the older dot form.
IIRCC you have to import the record to use that constructor, but with
the constructor fns you can :require them like any other clojure fn.
Not a big deal, but it is nicer and doesn't let the interop abstraction
bleed into your ns declarations.
2) Why is the third version not within a list? I thought that for the
language to consider something "callable" it had to be the first
argument in a list (eg : (+ 1 2))
Your third version is using tagged literals and so the semantics of the
reader is different in that case. See
http://clojure.org/reader#The%20Reader--extensible%20data%20notation%20(edn)
3) The record that is returned via (def b [version of choice goes
here]) is treated as a map when using the form (:title b) but doesn't
treat it as a map when using the form (b :title) which seems pretty
inconsistent to me; is there are valid reason for this inconsistency?
I'm sure I'm missing something.
I agree that it is inconsistent. I don't know why that inconsistency
exists but I would be curious to know the reason if someone on the list
knows... As A. Webb just pointed out you can add that behavior yourself
if you want to.
Thanks!
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Re: Questions regarding Map vs Record and usage
You can refer-in the first (factory function) to another namespace; for the
second you'd have to import the class. I prefer the first. The third is
special syntax for the reader.
As to the last question, I don't know, but it allows you to define your
own. For example,
(defrecord Book [title author]
clojure.lang.IFn
(invoke [this x] (get this x))
(invoke [this x not-found] (get this x not-found)))
(def b (->Book "Lord of the Rings", "Tolkien"))
(b :title) ;=> "Lord of the Rings"
But you could alter the behavior as desired.
On Wednesday, April 9, 2014 1:51:01 PM UTC-5, Anthony Ortiz wrote:
>
> I see that there are several ways of instantiating a record :
>
>
> (->Book "Lord of the Rings", "Tolkien")
>
> (Book. "Lord of the Rings", "Tolkien")
>
> #user.Book{:title "Lord of the Rings", :author "Tolkien"}
>
>
> Questions :
> 1) The second version is referred to as the "original" version so I'm
> wondering which is the preferred method.
> 2) Why is the third version not within a list? I thought that for the
> language to consider something "callable" it had to be the first argument
> in a list (eg : (+ 1 2))
> 3) The record that is returned via (def b [version of choice goes here])
> is treated as a map when using the form (:title b) but doesn't treat it as
> a map when using the form (b :title) which seems pretty inconsistent to me;
> is there are valid reason for this inconsistency? I'm sure I'm missing
> something.
>
> Thanks!
>
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Questions regarding Map vs Record and usage
I see that there are several ways of instantiating a record :
(->Book "Lord of the Rings", "Tolkien")
(Book. "Lord of the Rings", "Tolkien")
#user.Book{:title "Lord of the Rings", :author "Tolkien"}
Questions :
1) The second version is referred to as the "original" version so I'm
wondering which is the preferred method.
2) Why is the third version not within a list? I thought that for the
language to consider something "callable" it had to be the first argument
in a list (eg : (+ 1 2))
3) The record that is returned via (def b [version of choice goes here]) is
treated as a map when using the form (:title b) but doesn't treat it as a
map when using the form (b :title) which seems pretty inconsistent to me;
is there are valid reason for this inconsistency? I'm sure I'm missing
something.
Thanks!
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