Add cbrt and tests, update NEWS.md.

NEWS.md

@@ -15,7 +15,7 @@
    as well as return tuples of `Units` objects.
  - `@preferunit` has been replaced with a function `preferunits`.
  - Added some methods for `ustrip`.
- - Implement `typemin`, `typemax` for `Quantity`s.
+ - Implement `typemin`, `typemax`, `cbrt` for `Quantity`s.
  - Added matrix inversion for `StridedMatrix{T<:Quantity}`.
  - Added `istriu`, `istril` for `AbstractMatrix{T<:Quantity}`.
  - The `Unitful.SIUnits` module has been renamed to `Unitful.DefaultSymbols`.

src/Unitful.jl

@@ -13,7 +13,7 @@ end
 
 import Base: ==, <, <=, +, -, *, /, //, ^
 import Base: show, convert
-import Base: abs, abs2, float, fma, muladd, inv, sqrt
+import Base: abs, abs2, float, fma, muladd, inv, sqrt, cbrt
 import Base: min, max, floor, ceil, log, log10, real, imag, conj
 import Base: sin, cos, tan, cot, sec, csc, atan2, cis, vecnorm
 
@@ -671,23 +671,39 @@ for (_x,_y) in [(:fma, :_fma), (:muladd, :_muladd)]
 end
 
 sqrt(x::Quantity) = Quantity(sqrt(x.val), sqrt(unit(x)))
+cbrt(x::Quantity) = Quantity(cbrt(x.val), cbrt(unit(x)))
 
-# This is a generated function to ensure type stability and keep `sqrt` fast.
+# The following are generated functions to ensure type stability.
 @generated function sqrt(x::Dimensions)
     tup = x.parameters[1]
     tup2 = map(x->x^(1//2),tup)
     y = *(Dimensions{tup2}())    # sort appropriately
     :($y)
 end
 
-# This is a generated function to ensure type stability and keep `sqrt` fast.
 @generated function sqrt(x::Units)
     tup = x.parameters[1]
     tup2 = map(x->x^(1//2),tup)
     y = *(Units{tup2,()}())    # sort appropriately
     :($y)
 end
 
+# The following are generated functions to ensure type stability.
+@generated function cbrt(x::Dimensions)
+    tup = x.parameters[1]
+    tup2 = map(x->x^(1//3),tup)
+    y = *(Dimensions{tup2}())    # sort appropriately
+    :($y)
+end
+
+@generated function cbrt(x::Units)
+    tup = x.parameters[1]
+    tup2 = map(x->x^(1//3),tup)
+    y = *(Units{tup2,()}())    # sort appropriately
+    :($y)
+end
+
+
 for _y in (:sin, :cos, :tan, :cot, :sec, :csc, :cis)
     @eval ($_y)(x::DimensionlessQuantity) = ($_y)(uconvert(NoUnits, x))
 end

test/runtests.jl

@@ -302,6 +302,10 @@ end
         @test sqrt(4m^(2//3)) == 2m^(1//3)
         @test @inferred(sqrt(𝐋^2)) == 𝐋
         @test @inferred(sqrt(m^2)) == m
+        @test @inferred(cbrt(8m^3)) == 2m
+        @test cbrt(8m) == 2m^(1//3)
+        @test @inferred(cbrt(𝐋^3)) == 𝐋
+        @test @inferred(cbrt(m^3)) == m
         @test (2m)^3 == 8*m^3
         @test (8m)^(1//3) == 2*m^(1//3)
         @test @inferred(cis(90°)) ≈ im