For your "additional" question: no overhead for the abstract version versus the two specialized. Don't think of them as types like in C/C++ function definition, think of them as a filter. Julia will compile a new version for every type input you put in anyway that is specialized for the type parsed in.
On Tuesday, July 8, 2014 2:51:41 PM UTC-7, John Myles White wrote: > > What you're doing isn't a workaround: it's the correct way to do this in > the current version of Julia. There may be shorthand in the future, but > this is the right approach today. > > -- John > > On Jul 8, 2014, at 2:01 PM, Andrei Zh <[email protected] <javascript:>> > wrote: > > > Here's another question about code style. Let's say I want to write > function "inc()" that just adds 1 to its (typed) argument. For simple > numbers I can force parameter to be of type Number: > > > > julia> function inc(x::Number) x + 1 end > > inc (generic function with 1 method) > > > > julia> inc(1) > > 2 > > > > julia> inc(1.) > > 2.0 > > > > For parametrised collections, however, it doesn't work, since Julia's > type parameters are invariant: > > > > julia> function inc(x::Vector{Number}) x + 1 end > > inc (generic function with 2 methods) > > > > julia> inc([1, 2]) > > ERROR: no method inc(Array{Int64,1}) > > > > julia> inc([1., 2.]) > > ERROR: no method inc(Array{Float64,1}) > > > > As a workaround I use parametrized functions, which work just fine: > > > > julia> function inc{T <: Number}(x::Vector{T}) x + 1 end > > inc (generic function with 3 methods) > > > > julia> inc([1, 2]) > > 2-element Array{Int64,1}: > > 2 > > 3 > > > > julia> inc([1., 2.]) > > 2-element Array{Float64,1}: > > 2.0 > > 3.0 > > > > But since operations on vectors of (any) numbers are so common, I would > expect simpler / shorter way to write them. More generally, I wonder if > there's a better way to write functions with collections parametrized by > abstract classes. > > > > Additional (but closely related) question: is there any run-time > overhead for function arguments with abstract type parameters over several > functions with concrete types? E.g. is writing "inc(x::Vector{Int})" and > "inc(x::Vector{Float64})" faster than "function inc{T <: > Number}(x::Vector{T})"? > >
