[julia-users] Function `copyconvert`?

[gTcV]

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?