Instants and UUIDs

The values #inst and #uuid read as, on every backend. An instant is the oracle's java.util.Date, its milliseconds since 1970-01-01T00:00:00Z. It prints as #inst "..." in UTC under print and pr alike, and str of it is the oracle's toString in UTC (Wed Jan 01 00:00:00 UTC 2020). A UUID is the oracle's java.util.UUID: it prints as #uuid "...", and str of it is its lowercase spelling. Two of a kind are = when the oracle's are, compare orders them like the oracle (a UUID by its two halves as signed longs), a map or set finds one by =, and neither is a collection or a function. class answers :java.util.Date and :java.util.UUID, and a multimethod on class or a protocol dispatches on those classes. inst? and uuid? test the kinds, and clojure.instant also reads a timestamp into a java.sql.Timestamp or a java.util.Calendar.

The interop spellings make the same values, on every backend: (java.util.Date.) is the current instant, (java.util.Date. ms) and (java.sql.Timestamp. ms) the instant of those milliseconds, (java.util.UUID. msb lsb) the UUID of the two halves, UUID/randomUUID and UUID/fromString those of random-uuid and #uuid, and System/currentTimeMillis answers the milliseconds since the epoch. A Date's getTime, setTime (in place), before, after and compareTo, a Timestamp's getNanos and a UUID's halves, version and variant answer everywhere. On the interpreter and the JVM such a value crosses into a Java member as the host object ((.format sdf (java.util.Date.))), any other method of its class is the host object's ((.toInstant d)), and a host Date or UUID a member answers is = to it and compares beside it.

#inst "2020-06-15T08:20:30.456-00:00" Mon Jun 15 08:20:30 UTC 2020
true (#inst "1999-01-01T00:00:00.000-00:00" #inst "2020-06-15T08:20:30.456-00:00" #inst "2021-01-01T00:00:00.000-00:00")
#uuid "550e8400-e29b-41d4-a716-446655440000" :found

Differences

• class answers a keyword, like for every value (Deviations).
• str of an instant is the oracle's toString with its time zone UTC: the oracle answers it in its JVM's default time zone, which no wasm backend has.
• A UUID's hex digits are the ASCII ones, where the oracle's UUID.fromString also takes any Unicode decimal digit and the fullwidth Latin letters.
• A host java.util.Date, java.sql.Timestamp or java.util.UUID a Java member answers (interpreter and JVM) stays a host object: = to the value made here as the first one's equals decides, ordered beside it by compareTo, taken by inst?, uuid? and inst-ms (a java.time.Instant too), but it prints as #<java java.util.Date> and is another map key or set member than the value made here.
• (java.util.Date. s) of a string computed at run time is refused: the oracle's deprecated Date(String) parse is not here (a literal string still reaches the host's on the interpreter and the JVM). A Date's mutators but setTime (setYear, ...) are refused by name, where the oracle's Date changes.
• A clojure.instant Calendar has no host object: it never crosses into a Java member, and its class's methods are refused by name. On wasm, so is a method of a Date or UUID only the host answers (toInstant, hashCode).