map! to store result directly in collection instead of destination

[martincornejo]

The REPL documentation shows the following for the function map!

help?> map!
search: map! asyncmap! mapcols! map mapcols mapfoldr mapfoldl mapslices mapreduce

  map!(function, destination, collection...)

  Like map, but stores the result in destination rather than a new collection.      
  destination must be at least as large as the first collection.

  Examples
  ≡≡≡≡≡≡≡≡≡≡

  julia> a = zeros(3);
  
  julia> map!(x -> x * 2, a, [1, 2, 3]);
  
  julia> a
  3-element Array{Float64,1}:
   2.0
   4.0
   6.0

To my understanding the appended ! implies that the function modifies the input variable, but in this case it is stored in a separate destination argument while the collection remains unchanged. For now a simple map!(function, collection) is not supported. I can imagine in some cases the output will have a different size/structure to the input collection and then the map!(function, destination, collection) form is convenient.

Maybe the following example can highlight the current inconvenience.

julia> a = [1, 2, 3]
3-element Array{Int64,1}:
 1
 2
 3

julia> map!(x -> x * 2, a)
ERROR: BoundsError: attempt to access ()
  at index [1]
Stacktrace:
 [1] getindex(::Tuple, ::Int64) at .\tuple.jl:24
 [2] map_n!(::var"#41#42", ::Array{Int64,1}, ::Tuple{}) at .\abstractarray.jl:2122  
 [3] map!(::var"#41#42", ::Array{Int64,1}) at .\abstractarray.jl:2151
 [4] top-level scope at REPL[46]:1

julia> map!(x -> x * 2, a, a)
3-element Array{Int64,1}:
 2
 4
 6

[martincornejo]

The same might apply to broadcast!

help?> broadcast!
search: broadcast! broadcast Broadcast

  broadcast!(f, dest, As...)

  Like broadcast, but store the result of broadcast(f, As...) in the dest array.    
  Note that dest is only used to store the result, and does not supply arguments    
  to f unless it is also listed in the As, as in broadcast!(f, A, A, B) to perform  
  A[:] = broadcast(f, A, B).

  Examples
  ≡≡≡≡≡≡≡≡≡≡

  julia> A = [1.0; 0.0]; B = [0.0; 0.0];
  
  julia> broadcast!(+, B, A, (0, -2.0));
  
  julia> B
  2-element Array{Float64,1}:
    1.0
   -2.0
  
  julia> A
  2-element Array{Float64,1}:
   1.0
   0.0
  
  julia> broadcast!(+, A, A, (0, -2.0));
  
  julia> A
  2-element Array{Float64,1}:
    1.0
   -2.0

[tkf]

It seems like this is a dup of #31677.