Ideally I don't have to assume anything about the return value (all I care
about is the side effect).
On Tuesday, June 9, 2015 at 4:58:36 PM UTC-4, Scott T wrote:
>
> Not sue if this is exactly what you want, but you can achieve this with
> `map!` by making `add_one!` return the modified MyType:
>
> julia> type MyType; x::Int; end
>
> julia> function add_one!(mt::MyType)
> mt.x += 1
> return mt
> end
> add_one! (generic function with 1 method)
>
> julia> A = map(MyType, 1:3)
> 3-element Array{MyType,1}:
> MyType(1)
> MyType(2)
> MyType(3)
>
> julia> map!(add_one!, A)
> 3-element Array{MyType,1}:
> MyType(2)
> MyType(3)
> MyType(4)
>
> julia> A
> 3-element Array{MyType,1}:
> MyType(2)
> MyType(3)
> MyType(4)
>
>
>
>
>
> On Tuesday, 9 June 2015 20:39:11 UTC+1, Tom Breloff wrote:
>>
>> 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
>>
>>
>>
