4 ms·

Christophe Grand pointed out in the comments that a plain map should be used instead of a struct, so your example in Clojure would be: {:height 6.3 :age 63 :wei

by jb3 16y ago

Christophe Grand pointed out in the comments that a plain map should be used instead of a struct, so your example in Clojure would be: {:height 6.3 :age 63 :weight-in-kg 63}

deleted 16y ago
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mahmud 16y ago
That works in the short term, but beyond that, Clojure will need to resolve that issue. Records are not the same thing as hash-tables. A record, or struct, is a single unit value, while a hash-table, or map, is an aggregate container. There is an implicit contract in place; a record is guaranteed to have JUST the fields it's defined to have, while a map can grow at run time (are you going to test for the fields you want and ignore the rest? quack quack! you can't add fields to a record at runtime, so the two are NOT interchangeable. Equality is a transitive relation, while duck-typing is not.) A record is a generalization of the concept of "value" beyond data types immediately representable by machine. While a hash-table is a generalization of arrays, an aggregate of values, addressable by an index (hash-tables remedy the silly assumption that an index must be of an integral value.) To give an analogy; it's like asking what's the best way to group a bunch of papers (folder, envlope, binder) and then hearing someone suggest "bookshelf!". Again, OK short-term, but stinks. Fix the structs; even C has dot and arrow notations, making the field names clear.
- jkkramer 16y ago
  Records and structs can grow at runtime (insofar as immutable data structures grow). user> (defrecord Foo [x]) user.Foo user> (assoc (Foo. 1) :y 2) #:user.Foo{:x 1, :y 2} user> (defstruct foo :x) #'user/foo user> (assoc (struct-map foo :x 1) :y 2) {:x 1, :y 2}
  - mahmud 16y ago
    Well, what do you know, Clojure records and hash-tables are equal (strongly.) I will announce this great news to a few of my closest friends :-)
    - jkkramer 16y ago
      Almost. Record types are checked as part of full equality. So record Foo{:x 1} is not equal to Bar{:x 1} or to {:x 1}.
      - w01fe 16y ago
        Almost. Record types are checked as part of Clojure's "=", but not as part of Java's ".equals". See [1] and linked material. This means that Foo{:x 1} and Bar{:x 1} will collide in sets and as map keys (of Clojure or Java varieties). This seems a bit icky to me, but seems to be intentional. [1] http://dev.clojure.org/jira/browse/CLJ-736 http://dev.clojure.org/jira/browse/CLJ-736
    - lukev 16y ago
      Records also provide better performance than hash tables for their defined keys. You can think of them as a Java class that has certain fields (it's named fields) and also implements the Map interface for additional expandability. Records provide "accessor" methods for their named fields that provide bare-metal JVM performance.
- deleted 16y ago
  [deleted]

by jb3 16y ago

Christophe Grand pointed out in the comments that a plain map should be used instead of a struct, so your example in Clojure would be: {:height 6.3 :age 63 :weight-in-kg 63}

deleted 16y ago

[deleted]

mahmud 16y ago

That works in the short term, but beyond that, Clojure will need to resolve that issue. Records are not the same thing as hash-tables. A record, or struct, is a single unit value, while a hash-table, or map, is an aggregate container. There is an implicit contract in place; a record is guaranteed to have JUST the fields it's defined to have, while a map can grow at run time (are you going to test for the fields you want and ignore the rest? quack quack! you can't add fields to a record at runtime, so the two are NOT interchangeable. Equality is a transitive relation, while duck-typing is not.) A record is a generalization of the concept of "value" beyond data types immediately representable by machine. While a hash-table is a generalization of arrays, an aggregate of values, addressable by an index (hash-tables remedy the silly assumption that an index must be of an integral value.) To give an analogy; it's like asking what's the best way to group a bunch of papers (folder, envlope, binder) and then hearing someone suggest "bookshelf!". Again, OK short-term, but stinks. Fix the structs; even C has dot and arrow notations, making the field names clear.

jkkramer 16y ago
Records and structs can grow at runtime (insofar as immutable data structures grow). user> (defrecord Foo [x]) user.Foo user> (assoc (Foo. 1) :y 2) #:user.Foo{:x 1, :y 2} user> (defstruct foo :x) #'user/foo user> (assoc (struct-map foo :x 1) :y 2) {:x 1, :y 2}
- mahmud 16y ago
  Well, what do you know, Clojure records and hash-tables are equal (strongly.) I will announce this great news to a few of my closest friends :-)
  - jkkramer 16y ago
    Almost. Record types are checked as part of full equality. So record Foo{:x 1} is not equal to Bar{:x 1} or to {:x 1}.
    - w01fe 16y ago
      Almost. Record types are checked as part of Clojure's "=", but not as part of Java's ".equals". See [1] and linked material. This means that Foo{:x 1} and Bar{:x 1} will collide in sets and as map keys (of Clojure or Java varieties). This seems a bit icky to me, but seems to be intentional. [1] http://dev.clojure.org/jira/browse/CLJ-736 http://dev.clojure.org/jira/browse/CLJ-736
  - lukev 16y ago
    Records also provide better performance than hash tables for their defined keys. You can think of them as a Java class that has certain fields (it's named fields) and also implements the Map interface for additional expandability. Records provide "accessor" methods for their named fields that provide bare-metal JVM performance.
deleted 16y ago
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