Optimal way of using simple `map()` is by avoiding to use lambda function. So for example

```julia
dbl(x)=x*2
arr=rand(1000)
```

non-optimal method is significantly more expensive.
```
julia> @time map(dbl, arr);
  0.000090 seconds (7 allocations: 8.125 KB)
```

and by avoiding the use of lambda you get
```
julia> @time map(x->dbl(x), arr);
  0.040455 seconds (13.77 k allocations: 632.087 KB)
```