Discussion: https://github.com/JuliaLang/julia/issues/12441
On Thursday, July 21, 2016 at 2:49:19 PM UTC-4, gTcV wrote:
>
> I recently frequently encounter the situation where I need to both copy as
> well as optionally convert an object. It turns out `convert` on its own
> will not do the job in this case as it doesn't create a copy if the
> conversion is trivial:
>
> julia> v = Vector{Int}();
> julia> convert(Vector{Int}, v) === v
> true
> julia> convert(Vector{Float64}, v) === v
> false
>
> So to be safe I have to write `copy(convert(NewT,obj))`, but that creates
> two copies in case `NewT != obj` [1]. I assume this must be a fairly common
> problem, and I am surprised Julia doesn't offer a solution to it.
>
> The following is a first attempt at a solution, but I would not be
> surprised if there are edge cases where this approach fails.
>
> function copyconvert{T}(::Type{T}, x)
> y = convert(T,x)
> if y === x
> return copy(x)
> else
> return y
> end
> end
>
> [1] In C++, the compiler would optimise this case down to one copy ("copy
> elision"), but I assume the Julia compiler doesn't. Correct?
>
