# DateTime constructor that uses Date.value(x) as input

**URL:** <https://discourse.julialang.org/t/datetime-constructor-that-uses-date-value-x-as-input/7212>\
**Category:** General Usage\
**Tags:** dates\
**Created:** [November 21, 2017, 4:49am UTC](https://discourse.julialang.org/t/datetime-constructor-that-uses-date-value-x-as-input/7212 "2017-11-21T04:49:07Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![colintbowers](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/colintbowers/32/8033_2.png) [@colintbowers](https://discourse.julialang.org/u/colintbowers)\
**Post date:** [November 21, 2017, 4:49am UTC](https://discourse.julialang.org/t/datetime-constructor-that-uses-date-value-x-as-input/7212/1 "2017-11-21T04:49:07Z")

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Hi all,

I’m probably overlooking something obvious, but I can’t work out how to construct a `DateTime` using as input the `Int64` returned by `Dates.value()`. Note the following:

```julia
julia> dt = now()
2017-11-21T15:38:01.282

julia> i = Dates.value(dt)
63646961881282

julia> dt2 = DateTime(i)
132444472-12-19T17:48:18.304

```

Obviously `dt` is not equal to `dt2` since in the call `DateTime(i)`, the `i` is being interpreted as years, rather than milliseconds since epoch.

So how do I construct a `DateTime` using `i`, such that `dt` will equal `dt2`? I can see how I could divide `i` up into years, months, days, hours, minutes, seconds, milliseconds, but I’m fairly sure there must be a better method than this, given that `DateTime` is literally just an immutable wrapper on `i`.

Note that `DateTime(Base.Dates.UTInstant{Base.Dates.Millisecond}(i))` works, but also gives a deprecation warning which I found a bit confusing.

Incidentally, the reason why I might want to do this is so that I can write `DateTime` to a binary file, then read it back in later with minimum overhead.

Cheers,

Colin

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<div class="post-metadata">

**Author:** ![quinnj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/quinnj/32/11_2.png) [@quinnj](https://discourse.julialang.org/u/quinnj)\
**Post date:** [November 21, 2017, 5:01am UTC](https://discourse.julialang.org/t/datetime-constructor-that-uses-date-value-x-as-input/7212/2 "2017-11-21T05:01:03Z")

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> [@colintbowers](#):
>
> 63646961881282

You’ll want

```julia
julia> DateTime(Dates.UTInstant(Dates.Millisecond(i)))
2017-11-21T15:38:01.282

```

or for short

```julia
julia> DateTime(Dates.UTM(i))
2017-11-21T15:38:01.282

```

I agree this is pretty clunky and we should provide a better way to create a DateTime from the result of `Dates.value` .

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<div class="post-metadata">

**Author:** ![colintbowers](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/colintbowers/32/8033_2.png) [@colintbowers](https://discourse.julialang.org/u/colintbowers)\
**Post date:** [November 21, 2017, 5:39am UTC](https://discourse.julialang.org/t/datetime-constructor-that-uses-date-value-x-as-input/7212/3 "2017-11-21T05:39:02Z")

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Thanks for responding so quickly. `DateTime(Dates.UTM(i))` is definitely un-clunky enough for me! 🙂

Cheers,

Colin

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<div class="post-metadata">

**Author:** ![quinnj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/quinnj/32/11_2.png) [@quinnj](https://discourse.julialang.org/u/quinnj)\
**Post date:** [November 21, 2017, 5:45am UTC](https://discourse.julialang.org/t/datetime-constructor-that-uses-date-value-x-as-input/7212/4 "2017-11-21T05:45:32Z")

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We should at least improve the docs though 🙂