[julia-users] map without creating a new array

[Tom Breloff]

I'm probably overlooking something simple, but is there a built-in function 
to "apply" a function to each element of an abstract array without creating 
a new array?  This obviously only makes sense when you're updating an 
object as part of the function call. Here's an example below... does this 
exist in Base?  Should it?


julia> function map_without_result(f, A)
           for x in A
               f(x)
           end
       end
map_without_result (generic function with 1 method)

julia> type MyType; x::Int; end

julia> add_one!(mt::MyType) = mt.x += 1
add_one! (generic function with 1 method)

julia> A = map(MyType, 1:5)
10-element Array{MyType,1}:
 MyType(1) 
 MyType(2) 
 MyType(3) 
 MyType(4) 
 MyType(5) 

julia> map_without_result(add_one!, A)

julia> A
10-element Array{MyType,1}:
 MyType(2) 
 MyType(3) 
 MyType(4) 
 MyType(5) 
 MyType(6) 



Currently (on master from 5 days ago), "map(add_one!, A)" will return a new 
Vector{Int}, and "map!(add_one!, A)" gives an error:


julia> map(add_one!, A)
5-element Array{Int64,1}:
 3
 4
 5
 6
 7

julia> map!(add_one!, A)
ERROR: MethodError: `convert` has no method matching 
convert(::Type{MyType}, ::Int64)
This may have arisen from a call to the constructor MyType(...),
since type constructors fall back to convert methods.
Closest candidates are:
  MyType(::Int64)
  MyType(::Any)
  call{T}(::Type{T}, ::Any)
  ...
 in map! at abstractarray.jl:1447
 in map! at abstractarray.jl:1444