Details
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Type:
Improvement
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Status: Closed
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Priority:
Major
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Resolution: Declined
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Affects versions: None
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Fix versions: None
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Components: Core type system
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Labels:None
Description
A link to the instigating mailing list post: https://groups.google.com/forum/#!topic/clojure-core-typed/Af650Di0VT4.
The following is a sketch of what I think should be possible. (adapted from java.jdbc)
(typed/defprotocol Connectable
(add-connection [db connection :- java.sql.Connection] :- '{:connection java.sql.Connection})
(get-level [db] :- typed/AnyInteger))
(typed/extend-protocol Connectable
String
(add-connection [s connection] :- '{:connection java.sql.Connection
:connection-string String
:level '0}) ; Ideally, this type is inferred, but that seems like a separate enhancement.
{:connection connection :level 0 :connection-string s})
(get-level [_] 0)
(clojure.lang.Associative typed/Any typed/Any) ; N.B. this type could/should be made more precise, but I'm leaving it as is to keep the example focused.
(add-connection [m connection] (assoc m :connection connection))
(get-level [m] (or (:level m) 0))
nil
(add-connection [_ connection] {:connection connection :level 0 :legacy true})
(get-level [_] 0))
(typed/defn get-connection-string [s :- String, conn :- java.sql.Connection] :- String
(:connection-string (add-connection s conn)))
In particular, note how the body of get-connection-string "knows" that the value of (add-connection s conn) will contain a string for the key :connection-string.
