Switched isequal and hash to just use utc_datetime (#147)

* Switched `isequal` and `hash` to just use `utc_datetime`.

NOTE: This is a breaking change that'll make most of our lives easier
(e.g., joins with `DataFrame`s) :)

* PR review fixes.

src/types.jl

@@ -283,24 +283,20 @@ end
 # Equality
 ==(a::ZonedDateTime, b::ZonedDateTime) = a.utc_datetime == b.utc_datetime
 isless(a::ZonedDateTime, b::ZonedDateTime) = isless(a.utc_datetime, b.utc_datetime)
+isequal(a::ZonedDateTime, b::ZonedDateTime) = isequal(a.utc_datetime, b.utc_datetime)
 
-# Note: `hash` and `isequal` assume that the "zone" of a ZonedDateTime is not being set
-# incorrectly.
+"""
+    hash(::ZonedDateTime, h)
 
+Compute an integer hash code for a ZonedDateTime by hashing the `utc_datetime` field.
+`hash(:utc_instant, h)` is used to avoid collisions with `DateTime` hashes.
+"""
 function hash(zdt::ZonedDateTime, h::UInt)
+    h = hash(:utc_instant, h)
     h = hash(zdt.utc_datetime, h)
-    h = hash(zdt.timezone, h)
     return h
 end
 
-function isequal(a::ZonedDateTime, b::ZonedDateTime)
-    return (
-        isequal(a.utc_datetime, b.utc_datetime) &&
-        isequal(a.timezone, b.timezone) &&
-        isequal(a.zone, b.zone)
-    )
-end
-
 function ==(a::VariableTimeZone, b::VariableTimeZone)
     a.name == b.name && a.transitions == b.transitions
 end

test/conversions.jl

@@ -93,7 +93,7 @@ round_trip = TimeZones.unix2zdt(TimeZones.zdt2unix(Int64, zdt))
 zdt = ZonedDateTime(2010, 1, 2, 3, 4, 5, warsaw)
 round_trip = TimeZones.unix2zdt(TimeZones.zdt2unix(Int64, zdt))
 @test round_trip == zdt
-@test !isequal(round_trip, zdt)
+@test TimeZones.timezone(round_trip) != TimeZones.timezone(zdt)
 
 # Julian dates
 jd = 2457241.855

test/discovery.jl

@@ -41,10 +41,10 @@ paris = resolve("Europe/Paris", tzdata["europe"]...)
         expected_instant = ZonedDateTime(DateTime(2018, 3, 11, 8), wpg, zone)
         expected_valid = ZonedDateTime(2018, 3, 11, 3, wpg)
 
-        @test isequal(instant, expected_instant)
+        @test instant === expected_instant
         @test instant == expected_valid
-        @test !isequal(instant, expected_valid)
-        @test isequal(instant + Millisecond(0), expected_valid)
+        @test instant !== expected_valid
+        @test instant + Millisecond(0) === expected_valid
     end
 
     @testset "ambiguous" begin
@@ -54,10 +54,10 @@ paris = resolve("Europe/Paris", tzdata["europe"]...)
         expected_instant = ZonedDateTime(DateTime(2018, 11, 4, 7), wpg, zone)
         expected_valid = ZonedDateTime(2018, 11, 4, 1, wpg, 2)
 
-        @test isequal(instant, expected_instant)
+        @test instant === expected_instant
         @test instant == expected_valid
-        @test !isequal(instant, expected_valid)
-        @test isequal(instant + Millisecond(0), expected_valid)
+        @test instant !== expected_valid
+        @test instant + Millisecond(0) === expected_valid
     end
 
     @testset "upcoming" begin

test/types.jl

@@ -277,8 +277,8 @@ early_utc = ZonedDateTime(DateTime(UTM(typemin(Int64))), utc)
 @test spring_apia.zone == FixedTimeZone("SST", -39600, 0)
 @test spring_utc == spring_apia
 @test spring_utc !== spring_apia
-@test !isequal(spring_utc, spring_apia)
-@test hash(spring_utc) != hash(spring_apia)
+@test isequal(spring_utc, spring_apia)
+@test hash(spring_utc) == hash(spring_apia)
 @test astimezone(spring_utc, apia) === spring_apia  # Since ZonedDateTime is immutable
 @test astimezone(spring_apia, utc) === spring_utc
 @test isequal(astimezone(spring_utc, apia), spring_apia)
@@ -293,8 +293,8 @@ fall_apia = ZonedDateTime(DateTime(2010, 10, 1, 2), apia)
 @test fall_utc !== fall_apia
 @test !(fall_utc < fall_apia)
 @test !(fall_utc > fall_apia)
-@test !isequal(fall_utc, fall_apia)
-@test hash(fall_utc) != hash(fall_apia)
+@test isequal(fall_utc, fall_apia)
+@test hash(fall_utc) == hash(fall_apia)
 @test astimezone(fall_utc, apia) === fall_apia  # Since ZonedDateTime is immutable
 @test astimezone(fall_apia, utc) === fall_utc
 @test isequal(astimezone(fall_utc, apia), fall_apia)
@@ -311,6 +311,9 @@ y = deepcopy(x)
 @test isequal(x, y)
 @test hash(x) == hash(y)
 
+# Check that the ZonedDateTime and plain DateTimes don't hash to the same value.
+@test hash(x) != hash(y.utc_datetime)
+
 
 # A FixedTimeZone is effective for all of time where as a VariableTimeZone has as start.
 @test TimeZones.utc(early_utc) < apia.transitions[1].utc_datetime