Deprecate factorial(::Measurement) (#111)

Author: giordano

NEWS.md

@@ -8,6 +8,14 @@
   ([#103](https://github.com/JuliaPhysics/Measurements.jl/issues/103),
   [#104](https://github.com/JuliaPhysics/Measurements.jl/pull/104)).
 
+### Deprecations
+
+* `factorial(a::Measurement)` is deprecated in favour of
+  `SpecialFunctions.gamma(a + 1)`, as a result of
+  `SpecialFunctions.factorial(a::AbstractFloat)` being removed in
+  `SpecialFunctions.jl` v2.0
+  ([#111](https://github.com/JuliaPhysics/Measurements.jl/pull/111)).
+
 ## v2.6.0 (2021-04-20)
 
 ### New features

Project.toml

@@ -1,7 +1,7 @@
 name = "Measurements"
 uuid = "eff96d63-e80a-5855-80a2-b1b0885c5ab7"
 authors = ["Mosè Giordano <[email protected]>"]
-version = "2.6.0"
+version = "2.7.0"
 
 [deps]
 Calculus = "49dc2e85-a5d0-5ad3-a950-438e2897f1b9"

src/special-functions.jl

@@ -60,13 +60,7 @@ function SpecialFunctions.dawson(a::Measurement{T}) where {T<:AbstractFloat}
     return result(res, one(T) - 2 * aval * res, a)
 end
 
-# Factorial and gamma
-
-function SpecialFunctions.factorial(a::Measurement)
-    aval = a.val
-    fact = SpecialFunctions.factorial(aval)
-    return result(fact, fact*digamma(aval + one(aval)), a)
-end
+# Gamma
 
 function SpecialFunctions.gamma(a::Measurement)
     aval = a.val
@@ -226,3 +220,13 @@ function SpecialFunctions.besselkx(nu::Real, a::Measurement)
                   besselk(nu, x)*exp(x),
                   a)
 end
+
+# Deprecations
+function Base.factorial(a::Measurement)
+    Base.depwarn("""
+                 factorial(($(a))::Measurement) is deprecated, instead use
+                     SpecialFunctions.gamma($(a + one(a)))
+                 """,
+                 :factorial)
+    SpecialFunctions.gamma(a + one(a))
+end