Fix hint on mean(::Number, ::Number) (#131)

Author: LilithHafner

src/Statistics.jl

@@ -103,6 +103,16 @@ julia> mean(√, [1 2 3; 4 5 6], dims=2)
 """
 mean(f, A::AbstractArray; dims=:) = _mean(f, A, dims)
 
+function mean(f::Number, itr::Number)
+    f_value = try
+        f(itr)
+    catch MethodError
+        rethrow(ArgumentError("""mean(f, itr) requires a function and an iterable.
+                                 Perhaps you meant middle(x, y)?""",))
+    end
+    Base.reduce_first(+, f_value)/1
+end
+
 """
     mean!(r, v)
 

test/runtests.jl

@@ -171,6 +171,14 @@ end
     @test isnan(@inferred mean(Iterators.filter(x -> true, Int[])))
     @test isnan(@inferred mean(Iterators.filter(x -> true, Float32[])))
     @test isnan(@inferred mean(Iterators.filter(x -> true, Float64[])))
+
+    # using a number as a "function"
+    @test_throws "ArgumentError: mean(f, itr) requires a function and an iterable.\nPerhaps you meant middle(x, y)" mean(1, 2)
+    struct T <: Number
+        x::Int
+    end
+    (t::T)(y) = t.x * y
+    @test @inferred mean(T(2), 3) === 6.0
 end
 
 @testset "mean/median for ranges" begin