Add support for Dates.FixedPeriod and Dates.CompoundPeriod (#331)

* Add support for Dates.FixedPeriod * Fix tests on Julia < 1.2 * Fix more tests * Delete unused method * Add some more tests * Fix tests on 32-bit master * Add three-argument div * Add support for CompoundPeriod * Fix tests on 32bit * Add Quantity(::FixedPeriod) docstring * Fix some tests * Fix a test * Add documentation page
PainterQubits · Feb 26, 2021 · d4e15b5 · d4e15b5
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diff --git a/Project.toml b/Project.toml
@@ -4,6 +4,7 @@ version = "1.6.0"
 
 [deps]
 ConstructionBase = "187b0558-2788-49d3-abe0-74a17ed4e7c9"
+Dates = "ade2ca70-3891-5945-98fb-dc099432e06a"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 

diff --git a/docs/Project.toml b/docs/Project.toml
@@ -1,4 +1,5 @@
 [deps]
+Dates = "ade2ca70-3891-5945-98fb-dc099432e06a"
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
 Latexify = "23fbe1c1-3f47-55db-b15f-69d7ec21a316"
 Markdown = "d6f4376e-aef5-505a-96c1-9c027394607a"

diff --git a/docs/make.jl b/docs/make.jl
@@ -1,4 +1,4 @@
-using Documenter, Unitful
+using Documenter, Unitful, Dates
 
 DocMeta.setdocmeta!(Unitful, :DocTestSetup, :(using Unitful))
 
@@ -17,6 +17,7 @@ makedocs(
         "How units are displayed" => "display.md"
         "Logarithmic scales" => "logarithm.md"
         "Temperature scales" => "temperature.md"
+        "Interoperability with `Dates`" => "dates.md"
         "Extending Unitful" => "extending.md"
         "Troubleshooting" => "trouble.md"
         "License" => "LICENSE.md"

diff --git a/docs/src/dates.md b/docs/src/dates.md
@@ -0,0 +1,133 @@
+```@meta
+DocTestSetup = quote
+    using Unitful
+end
+```
+# Interoperability with the `Dates` standard library
+
+[Julia's `Dates` standard library](https://docs.julialang.org/en/v1/stdlib/Dates/) provides data types for representing specific points in time `Date`/`DateTime` and differences between them, i.e., periods. Unitful provides methods for using period types from the `Dates` standard library together with `Quantity`s.
+
+## Support for `Dates.FixedPeriod`s
+
+The `Dates.FixedPeriod` union type includes all `Dates.Period`s that represent a fixed period of time, i.e., `Dates.Week`, `Dates.Day`, `Dates.Hour`, `Dates.Minute`, `Dates.Second`, `Dates.Millisecond`, `Dates.Microsecond`, and `Dates.Nanosecond`. These types can be converted to `Quantity`s or used in place of them.
+
+!!! note
+    `Dates.Year` does not represent a fixed period and cannot be converted to a `Quantity`. While Unitful's `yr` unit is exactly equal to 365.25 days, a `Dates.Year` may contain 365 or 366 days.
+
+Each `FixedPeriod` is considered equivalent to a `Quantity`. For example, `Dates.Millisecond(5)` corresponds to the quantity `Int64(5)*u"ms"`. A `FixedPeriod` can be converted to the equivalent `Quantity` with a constructor:
+
+```@docs
+Unitful.Quantity(::Dates.FixedPeriod)
+```
+
+In most respects, `FixedPeriod`s behave like their equivalent quantities. They can be converted to other units using `uconvert`, used in arithmetic operations with other quantities, and they have a `unit` and `dimension`:
+
+```jldoctest
+julia> using Dates: Hour
+
+julia> p = Hour(3)
+3 hours
+
+julia> uconvert(u"s", p)
+10800 s
+
+julia> p == 180u"minute"
+true
+
+julia> p < 1u"d"
+true
+
+julia> 5u"s" + p
+10805 s
+
+julia> 210u"km" / p
+70.0 km hr^-1
+
+julia> unit(p) === u"hr"
+true
+
+julia> dimension(p)
+𝐓
+```
+
+Conversely, a `FixedPeriod` can be created from a quantity using the appropriate constructor, `convert`, or `round` methods. This will fail (i.e., throw an `InexactError`) if the resulting value cannot be represented as an `Int64`:
+
+```jldoctest
+julia> using Dates: Day, Hour, Millisecond
+
+julia> Millisecond(1.5u"s")
+1500 milliseconds
+
+julia> convert(Hour, 1u"yr")
+8766 hours
+
+julia> Day(1u"yr")
+ERROR: InexactError: Int64(1461//4)
+[...]
+
+julia> round(Day, 1u"yr")
+365 days
+```
+
+## Support for `Dates.CompoundPeriod`s
+
+The `Dates` standard library provides the `Dates.CompoundPeriod` type to represent sums of periods of different types:
+
+```@repl
+using Dates: Day, Second
+Day(5) + Second(1)
+typeof(ans)
+```
+
+Unitful provides facilities to work with `CompoundPeriod`s as long as they consist only of `FixedPeriod`s. Such `CompoundPeriod`s can be converted to `Quantity`s using `convert`, `uconvert`, or `round`:
+
+```@jldoctest
+julia> using Dates: Day, Second
+
+julia> p = Day(5) + Second(1)
+5 days, 1 second
+
+julia> uconvert(u"s", p)
+432001//1 s
+
+julia> convert(typeof(1.0u"yr"), p)
+0.01368928562374832 yr
+
+julia> round(u"d", p)
+5//1 d
+
+julia> q = Month(1) + Day(1)  # Month is not a fixed period
+1 month, 1 day
+
+julia> uconvert(u"s", q)
+ERROR: MethodError: no method matching Quantity{Rational{Int64},𝐓,Unitful.FreeUnits{(s,),𝐓,nothing}}(::Month)
+[...]
+```
+
+However, not all operations that are defined for `FixedPeriod`s support `CompoundPeriod`s as well.
+The reason for that is that a `CompoundPeriod` does not correspond to a specific unit:
+
+```@jldoctest
+julia> p = Day(365) + Hour(6)
+365 days, 6 hours
+
+julia> unit(p)  # A CompoundPeriod does not have a corresponding unit ...
+ERROR: MethodError: no method matching unit(::Dates.CompoundPeriod)
+[...]
+
+julia> dimension(p)  # ... but it does have a dimension
+𝐓
+
+julia> Quantity(p)  # As a result, there is no Quantity type associated with it ...
+ERROR: MethodError: no method matching Quantity(::Int64)
+[...]
+
+julia> T = typeof(1.0u"hr"); T(p)  # ... but it can be converted to a concrete time quantity
+8766.0 hr
+```
+
+Consequently, any operation whose result would depend on the input unit is not supported by `CompoundPeriod`s. For example:
+
+* `+(::Quantity, ::CompoundPeriod)` and `+(::CompoundPeriod, ::Quantity)` error, since the unit of the result depends on the units of both arguments.
+* `div(::Quantity, ::CompoundPeriod)` and `div(::CompoundPeriod, ::Quantity)` work, since the result is a dimensionless number.
+* `mod(::CompoundPeriod, ::Quantity)` works, but `mod(::Quantity, ::CompoundPeriod)` does not, since the second argument determines the unit of the returned quantity.
diff --git a/src/Unitful.jl b/src/Unitful.jl
@@ -20,6 +20,7 @@ import Base: steprange_last, unsigned
     import Base: isunordered
 end
 
+import Dates
 import LinearAlgebra: Diagonal, Bidiagonal, Tridiagonal, SymTridiagonal
 import LinearAlgebra: istril, istriu, norm
 import Random
@@ -67,5 +68,6 @@ include("fastmath.jl")
 include("logarithm.jl")
 include("complex.jl")
 include("pkgdefaults.jl")
+include("dates.jl")
 
 end
diff --git a/src/dates.jl b/src/dates.jl
@@ -0,0 +1,188 @@
+# Conversion from and to types from the `Dates` stdlib
+
+# Dates.FixedPeriod
+
+for (period, unit) = ((Dates.Week, wk), (Dates.Day, d), (Dates.Hour, hr),
+                      (Dates.Minute, minute), (Dates.Second, s), (Dates.Millisecond, ms),
+                      (Dates.Microsecond, μs), (Dates.Nanosecond, ns))
+    @eval unit(::Type{$period}) = $unit
+    @eval (::Type{$period})(x::AbstractQuantity) = $period(ustrip(unit($period), x))
+end
+
+dimension(p::Dates.FixedPeriod) = dimension(typeof(p))
+dimension(::Type{<:Dates.FixedPeriod}) = 𝐓
+
+"""
+    unit(x::Dates.FixedPeriod)
+    unit(x::Type{<:Dates.FixedPeriod})
+
+Return the units that correspond to a particular period.
+
+# Examples
+
+```julia
+julia> unit(Second(15)) == u"s"
+true
+
+julia> unit(Hour) == u"hr"
+true
+```
+"""
+unit(p::Dates.FixedPeriod) = unit(typeof(p))
+
+numtype(x::Dates.FixedPeriod) = numtype(typeof(x))
+numtype(::Type{T}) where {T<:Dates.FixedPeriod} = Int64
+
+quantitytype(::Type{T}) where {T<:Dates.FixedPeriod} =
+    Quantity{numtype(T),dimension(T),typeof(unit(T))}
+
+ustrip(p::Dates.FixedPeriod) = Dates.value(p)
+
+"""
+    Quantity(period::Dates.FixedPeriod)
+
+Create a `Quantity` that corresponds to the given `period`. The numerical value of the
+resulting `Quantity` is of type `Int64`.
+
+# Example
+
+```jldoctest
+julia> using Dates: Second
+
+julia> Quantity(Second(5))
+5 s
+```
+"""
+Quantity(period::Dates.FixedPeriod) = Quantity(ustrip(period), unit(period))
+
+uconvert(u::Units, period::Dates.FixedPeriod) = uconvert(u, Quantity(period))
+
+(T::Type{<:AbstractQuantity})(period::Dates.FixedPeriod) = T(Quantity(period))
+
+convert(T::Type{<:AbstractQuantity}, period::Dates.FixedPeriod) = T(period)
+convert(T::Type{<:Dates.FixedPeriod}, x::AbstractQuantity) = T(x)
+
+round(T::Type{<:Dates.FixedPeriod}, x::AbstractQuantity, r::RoundingMode=RoundNearest) =
+    T(round(numtype(T), ustrip(unit(T), x), r))
+round(u::Units, period::Dates.FixedPeriod, r::RoundingMode=RoundNearest; kwargs...) =
+    round(u, Quantity(period), r; kwargs...)
+round(T::Type{<:Number}, u::Units, period::Dates.FixedPeriod, r::RoundingMode=RoundNearest;
+      kwargs...) = round(T, u, Quantity(period), r; kwargs...)
+round(T::Type{<:AbstractQuantity}, period::Dates.FixedPeriod, r::RoundingMode=RoundNearest;
+      kwargs...) = round(T, Quantity(period), r; kwargs...)
+
+for (f, r) in ((:floor,:RoundDown), (:ceil,:RoundUp), (:trunc,:RoundToZero))
+    @eval $f(T::Type{<:Dates.FixedPeriod}, x::AbstractQuantity) = round(T, x, $r)
+    @eval $f(u::Units, period::Dates.FixedPeriod; kwargs...) =
+        round(u, period, $r; kwargs...)
+    @eval $f(T::Type{<:Number}, u::Units, period::Dates.FixedPeriod; kwargs...) =
+        round(T, u, period, $r; kwargs...)
+    @eval $f(T::Type{<:AbstractQuantity}, period::Dates.FixedPeriod; kwargs...) =
+        round(T, period, $r; kwargs...)
+end
+
+for op = (:+, :-, :*, :/, ://, :fld, :cld, :mod, :rem, :atan,
+          :(==), :isequal, :<, :isless, :≤)
+    @eval $op(x::Dates.FixedPeriod, y::AbstractQuantity) = $op(Quantity(x), y)
+    @eval $op(x::AbstractQuantity, y::Dates.FixedPeriod) = $op(x, Quantity(y))
+end
+for op = (:*, :/, ://)
+    @eval $op(x::Dates.FixedPeriod, y::Units) = $op(Quantity(x), y)
+    @eval $op(x::Units, y::Dates.FixedPeriod) = $op(x, Quantity(y))
+end
+div(x::Dates.FixedPeriod, y::AbstractQuantity, r...) = div(Quantity(x), y, r...)
+div(x::AbstractQuantity, y::Dates.FixedPeriod, r...) = div(x, Quantity(y), r...)
+
+isapprox(x::Dates.FixedPeriod, y::AbstractQuantity; kwargs...) =
+    isapprox(Quantity(x), y; kwargs...)
+isapprox(x::AbstractQuantity, y::Dates.FixedPeriod; kwargs...) =
+    isapprox(x, Quantity(y); kwargs...)
+
+function isapprox(x::AbstractArray{<:AbstractQuantity}, y::AbstractArray{T};
+                  kwargs...) where {T<:Dates.Period}
+    if isconcretetype(T)
+        y′ = reinterpret(quantitytype(T), y)
+    else
+        y′ = Quantity.(y)
+    end
+    isapprox(x, y′; kwargs...)
+end
+isapprox(x::AbstractArray{<:Dates.FixedPeriod}, y::AbstractArray{<:AbstractQuantity};
+         kwargs...) = isapprox(y, x; kwargs...)
+
+Base.promote_rule(::Type{Quantity{T,𝐓,U}}, ::Type{S}) where {T,U,S<:Dates.FixedPeriod} =
+    promote_type(Quantity{T,𝐓,U}, quantitytype(S))
+
+# Dates.CompoundPeriod
+
+dimension(p::Dates.CompoundPeriod) = dimension(typeof(p))
+dimension(::Type{<:Dates.CompoundPeriod}) = 𝐓
+
+uconvert(u::Units, period::Dates.CompoundPeriod) =
+    Quantity{promote_type(Int64,typeof(convfact(u,ns))),dimension(u),typeof(u)}(period)
+
+try_uconvert(u::Units, period::Dates.CompoundPeriod) = nothing
+function try_uconvert(u::TimeUnits, period::Dates.CompoundPeriod)
+    T = Quantity{promote_type(Int64,typeof(convfact(u,ns))),dimension(u),typeof(u)}
+    val = zero(T)
+    for p in period.periods
+        p isa Dates.FixedPeriod || return nothing
+        val += T(p)
+    end
+    val
+end
+
+(T::Type{<:AbstractQuantity})(period::Dates.CompoundPeriod) =
+    mapreduce(T, +, period.periods, init=zero(T))
+
+convert(T::Type{<:AbstractQuantity}, period::Dates.CompoundPeriod) = T(period)
+
+round(u::Units, period::Dates.CompoundPeriod, r::RoundingMode=RoundNearest; kwargs...) =
+    round(u, uconvert(u, period), r; kwargs...)
+round(T::Type{<:Number}, u::Units, period::Dates.CompoundPeriod,
+      r::RoundingMode=RoundNearest; kwargs...) =
+    round(T, u, uconvert(u, period), r; kwargs...)
+round(T::Type{<:AbstractQuantity}, period::Dates.CompoundPeriod,
+      r::RoundingMode=RoundNearest; kwargs...) =
+    round(T, T(period), r; kwargs...)
+
+for (f, r) in ((:floor,:RoundDown), (:ceil,:RoundUp), (:trunc,:RoundToZero))
+    @eval $f(u::Units, period::Dates.CompoundPeriod; kwargs...) =
+        round(u, period, $r; kwargs...)
+    @eval $f(T::Type{<:Number}, u::Units, period::Dates.CompoundPeriod; kwargs...) =
+        round(T, u, period, $r; kwargs...)
+    @eval $f(T::Type{<:AbstractQuantity}, period::Dates.CompoundPeriod; kwargs...) =
+        round(T, period, $r; kwargs...)
+end
+
+for op = (:fld, :cld, :atan, :<, :isless, :≤)
+    @eval $op(x::Dates.CompoundPeriod, y::AbstractQuantity) = $op(uconvert(unit(y),x), y)
+    @eval $op(x::AbstractQuantity, y::Dates.CompoundPeriod) = $op(x, uconvert(unit(x),y))
+end
+div(x::Dates.CompoundPeriod, y::AbstractQuantity, r...) = div(uconvert(unit(y),x), y, r...)
+div(x::AbstractQuantity, y::Dates.CompoundPeriod, r...) = div(x, uconvert(unit(x),y), r...)
+mod(x::Dates.CompoundPeriod, y::AbstractQuantity) = mod(uconvert(unit(y),x), y)
+rem(x::Dates.CompoundPeriod, y::AbstractQuantity) = rem(uconvert(unit(y),x), y)
+for op = (:(==), :isequal)
+    @eval $op(x::Dates.CompoundPeriod, y::AbstractQuantity{T,𝐓,U}) where {T,U} =
+        $op(try_uconvert(U(), x), y)
+    @eval $op(x::AbstractQuantity{T,𝐓,U}, y::Dates.CompoundPeriod) where {T,U} =
+        $op(x, try_uconvert(U(), y))
+end
+
+isapprox(x::Dates.CompoundPeriod, y::AbstractQuantity; kwargs...) =
+    dimension(y) === 𝐓 ? isapprox(uconvert(unit(y), x), y; kwargs...) : false
+isapprox(x::AbstractQuantity, y::Dates.CompoundPeriod; kwargs...) =
+    dimension(x) === 𝐓 ? isapprox(x, uconvert(unit(x), y); kwargs...) : false
+
+function isapprox(x::AbstractArray{<:AbstractQuantity},
+                  y::AbstractArray{Dates.CompoundPeriod}; kwargs...)
+    if dimension(eltype(x)) === 𝐓
+        isapprox(x, uconvert.(unit(eltype(x)), y); kwargs...)
+    else
+        false
+    end
+end
+
+isapprox(x::AbstractArray{Dates.CompoundPeriod}, y::AbstractArray{<:AbstractQuantity};
+         kwargs...) = isapprox(y, x; kwargs...)