Prevent overflow in mean(::AbstractRange)

and relax type constraint

src/Statistics.jl

@@ -197,9 +197,9 @@ if !isdefined(Base, :mean)
         end
     end
 
-    function mean(r::AbstractRange{<:Real})
-        isempty(r) && return oftype((first(r) + last(r)) / 2, NaN)
-        (first(r) + last(r)) / 2
+    function mean(r::AbstractRange{T}) where T
+        isempty(r) && return zero(T) / 0
+        return first(r) / 2 + last(r) / 2
     end
 end
 

test/runtests.jl

@@ -194,8 +194,16 @@ end
             @test f(2:0.1:n) ≈ f([2:0.1:n;])
         end
     end
-    @test mean(2:1) === NaN
-    @test mean(big(2):1) isa BigFloat
+    @test mean(2:0.1:4) === 3.0  # N.B. mean([2:0.1:4;]) != 3
+    @test mean(LinRange(2im, 4im, 21)) === 3.0im
+    @test mean(2:1//10:4) === 3//1
+    @test isnan(@inferred(mean(2:1))::Float64)
+    @test isnan(@inferred(mean(big(2):1))::BigFloat)
+    z = @inferred(mean(LinRange(2im, 1im, 0)))::ComplexF64
+    @test isnan(real(z)) & isnan(imag(z))
+    @test_throws DivideError mean(2//1:1)
+    @test mean(typemax(Int):typemax(Int)) === float(typemax(Int))
+    @test mean(prevfloat(Inf):prevfloat(Inf)) === prevfloat(Inf)
 end
 
 @testset "var & std" begin