at(dt::DateTime, t::Time) and at(d::Date, t::Time)

[scls19fr]

Hello,

Julia now have a Time type thanks to @aviks issue #12140 and @quinnj PR #12274

but a function that returns DateTime at a given Time (from either a Date or a DateTime)
could be a nice feature to have.

Usage example :
with DateTime

julia> dt = DateTime(2010, 1, 3, 20, 30)
2010-01-03T20:30:00

julia> at(dt, Dates.Time(13, 30))
2010-01-03T13:30:00

with Date

julia> d = Date(2010, 1, 1)
2010-01-03
julia> at(dt, Dates.Time(13, 30))
2010-01-03T13:30:00

This is a bit out of the scope of this issue but creating a DateTime from Date and Time is not as easy as it should be

julia> dt = DateTime(2010, 1, 3, 20, 30)
2010-01-03T20:30:00

julia> d = Date(dt)
2010-01-03

julia> t = Dates.Time(dt)
20:30:00

julia> DateTime(d, t)
ERROR: MethodError: Cannot `convert` an object of type Base.Dates.Time to an object of type Int64
This may have arisen from a call to the constructor Int64(...),
since type constructors fall back to convert methods.
Stacktrace:
 [1] DateTime(::Date, ::Base.Dates.Time) at ./dates/types.jl:311

Kind regards

[scls19fr]

Here is a possible implementation

julia> DateTime(d::Date, t::Dates.Time) = d + t
DateTime (generic function with 1 method)

julia> at(d::Dates.TimeType, t::Dates.Time) = DateTime(Date(d), t)
at (generic function with 1 method)

julia> dt = Dates.DateTime(2010, 1, 3, 20, 30)
2010-01-03T20:30:00

julia> d = Date(dt)
2010-01-03

julia> t = Dates.Time(dt)
20:30:00

julia> t2 = Dates.Time(22, 30)
22:30:00

julia> println(at(d, t2))
2010-01-03T22:30:00

julia> println(at(dt, t2))
2010-01-03T22:30:00

I hope that (one day) function chaining issue will be fixed #5571
so it could be possible to do something like

d.at(t)

or

d |> at(t)

or (but not my prefered syntaxic sugar)

d |> at(_, t)