When to return NaN vs throw an Error?

[CameronBieganek]

@Alec_Loudenback

positive = sum(x for x in v if x > 0)

As a side note, this code will throw an error on Julia 1.3 or earlier if v does not contain any positive numbers. See this thread:

Inconsistency in `sum` of an empty generator

On Julia 1.3, the following two empty generators both throw an error when you apply sum to them: julia> g1 = (1 for i in Int[]); julia> g2 = (x for x in [-1] if x > 0); julia> eltype(g1) Any julia> eltype(g2) Any julia> sum(g1) ERROR: ArgumentError: reducing over an empty collection is not allowed julia> sum(g2) ERROR: ArgumentError: reducing over an empty collection is not allowed That seems like the correct behavior. On newer versions of Julia, you can avoid the error by setting the ini…