auto: useful, annoying or bad practice?

[Jonathan M Davis]

On Sunday, May 20, 2018 14:33:16 I love Ice Cream via Digitalmars-d wrote:
> On Sunday, 20 May 2018 at 02:34:38 UTC, Neia Neutuladh wrote:
> > The return type for range-oriented functions in std.algorithm
> > is usually not terribly useful.
>
> So the first question that comes to my mind are what are the
> 'rules' of the output. Which is really what typing is. It's a
> series of rules. Your object is allowed to call these
> methods/properties. It is 'this' size. Languages have generic
> returns. D is not the only language with a concept of returning a
> 'compiler determined type'. But the rules are always baked into
> the API. If it's not, it's a design failure and more thought
> should be put into it.
>
> The only place I wouldn't be so strict with auto returns is in
> private methods. However, I still might tell someone to think
> about what they are trying to return there. It's not an
> unimportant piece of the API.

That's where you get into a combination of needing good documentation and
needing to know what set of traits to use to test the type to see what
functionality it has. But for better or worse, asking a type what it can do
is a key piece of Design by Introspection. The result can be extremely
powerful, as Andrei has talked about on multiple occasions (I'd suggest
watching his dconf 2015 talk about it if you haven't), but it does place a
higher burden on the programmer to figure out how to use a type. So, there
are pros and cons. Ultimately, auto can be extemely useful, and much of what
we do with D really wouldn't be reasonably feasible without it, but it also
needs to be used intelligently, because while it does bring some serious
benefits, it can be at the cost of clarity if used poorly.

- Jonathan M Davis