Momentary Eh?! for a Dynamic Language Programmmer. Tuples vs Arrays. Just rambling.

[Ary Borenszweig via Digitalmars-d-learn]

On 6/23/14, 6:18 PM, John Carter wrote:
> I guess between perl and Ruby and Scheme etc. I got used to creating
> hybrid containers....
>
> Want a pair of [string, fileList]? Just make an Array with two items,
> one a string, one and array of strings. Done.
>
> D barfed... leaving me momentarily stunned... then Oh Yes, type safety,
> Tuple's are the answer where Tuples where Tuples...
>
> Eventually found http://dlang.org/tuple.html and more specifically the
> somewhat unexpectedly named http://dlang.org/phobos/std_typecons.html
> and off I went...
>
> I do have a personal design guideline of when you adding too much
> behaviour to a heterocontainer, refactor into a class.
>
> But I guess I have never realised how often I do casually create
> heterogenous containers....
>
> Just rambling and musing.

Union types are very common (I use them every day), and IMHO it's very 
nice to have them included in the language (either built-in or as a 
library solution). As a library solution I would do something like this:

Union!(int, string)[] elements;
elements ~= 1;
elements ~= "hello";

auto x = elements[0].cast!(int);
// etc.

The difference with Variant is that (I think) Variant allows any kind of 
type to be inserted into it, but for a Union you are just limited to a 
set of types. For example, the following would be a compile-time error:

elements[0].cast!(float); // error, Union!(int, string) doesn't include 
float

As a built-in way the way to use it would be much nicer, but of course 
it involves too many changes for that to happen...