On 03/06/2014 03:21 AM, Edwin van Leeuwen wrote:

> Lately in C++ I have become a fan of the type of functional programming
> discussed here:
> http://blog.knatten.org/2012/11/02/efficient-pure-functional-programming-in-c-using-move-semantics/ 


I haven't read that yet but I have always returned a vector from a function that produced it instead of adding to a reference parameter.

> and was wondering if something similar is possible in D.

Most of the time it is automatic and a non-issue for arrays.

> Basically the idea is to define functions as follows:
>
> std::vector<double> add_to_vector( double x, std::vector<double> &&v ) {
>   v.push_back(x);
>   return v;
> }

Actually, when the name of the function is add_to_vector() anyway, there is an obvious side-effect. So, I would not return the result in C++.

However, when the name is like make_vector() then I always return the result. The alternatives have many hard questions to answer:

void make_vector(vector<double> & v)
{
    // Should I clear v first?
    // Should I simply start appending to v?
    // etc.
}

All of the efficiency of doing that goes out the window when one considers exception safety.

Anyway... Too much off topic... :)

> Is this possible in D?

T[] append(T)(T[] arr, T value)
{
    arr ~= value;
    return arr;
}

Done. :) Slices consist of two members that are cheap to copy: The number of elements and the pointer to the first element. It is already as efficient as move in C++.

You should also read the following article:

  http://dlang.org/d-array-article.html

Ali