On Apr 29, 2014, at 8:28 AM, Oliver Woodford <oliver.woodf...@gmail.com> wrote: > > Are you saying that f{T<:Real}(a::Array{T}) covers both homogeneous and > heterogeneous arrays, whereas f(a::Array{Real}) only covers heterogeneous > arrays? If that's the case it strikes me as just as confusing.
This is indeed how parametric types work in Julia. Array{T} is a family of types, one for each value of T. Defining f{T}(a::Array{T}) allows you to generically define an infinite number of functions -- you get a unique function for each value of T. In contrast, Array{Real} is a single type -- specifically, the type generated by the parametric type Array{T} when its parameter T = Real. There is no variable T, so f(a::Array{Real}) defines exactly one function -- and that function accepts exactly one type of input. Array{Any} is also a single type. -- John