Crystal: Weird time comparison result

[vladfaust]

Looking for a way to store exact time to Redis and to be able check it against original. What I've got for now:

t1 = Time.now.to_utc
t2 = Time.epoch_ms(t1.epoch_ms)
p "#{t1.inspect} == #{t2.inspect} = #{t1 == t2}"
# => "2017-09-01 21:28:15 UTC == 2017-09-01 21:28:15 UTC = false"

How should one properly store time to Redis and, important, to test it?

[vladfaust]

struct Time
  def ==(other : self)
    self.epoch_ms == other.epoch_ms
  end
end

Makes it work. Maybe worths adding to stdlib?

[oesgalha]

The comparison is based on time ticks, so you can store the amount of ticks to instantiate the exact same Time later:
````crystal
t1 = Time.now.to_utc
t2 = Time.new(t1.ticks).to_utc
p "#{t1.inspect} == #{t2.inspect} = #{t1 == t2}"

=> "2017-09-01 22:13:48 UTC == 2017-09-01 22:13:48 UTC = true"

Or if you want/need to store milliseconds you can extract the milliseconds from the diff of the 2 times and check if it's zero: crystal
t1 = Time.now.to_utc
t2 = Time.epoch_ms(t1.epoch_ms)
puts (t1 - t2).milliseconds == 0 #=> true
````

Note that if you instantiate two different Times using the same value for epoch_ms your initial example will work as expected:

t1 = Time.now.to_utc

t2 = Time.epoch_ms(t1.epoch_ms)
t3 = Time.epoch_ms(t1.epoch_ms)

p "#{t2.inspect} == #{t3.inspect} = #{t2 == t3}" #=> "2017-09-01 22:50:55 UTC == 2017-09-01 22:50:55 UTC = true"

[vladfaust]

@oesgalha ticks returns an extra-weird values like 636399139551521680, which will look strange for another developer (former Rubyists at least); (t1 - t2).milliseconds == 0 doesn't work for cases when need to assert equality of structs with Time as attribute.

But I see. Comparing by ticks - okay, as creators wish. They lead the way.

[RX14]

Well you have created 2 time instances which don't refer to the same time - you've lost precision by converting to the nearest millisecond with epoch_ms - so obviously they aren't equal.

[vladfaust]

@RX14 what's the exact precision of a tick?

[RX14]

One tenth of a microsecond, so 100ns. There are 10000 of them in a ms.