D's auto keyword

[Pelle Månsson]

On 01/13/2010 06:19 PM, dsimcha wrote:
> == Quote from Justin Johansson (no at spam.com)'s article
>> Happy New Year 2010 Everybody.
>> Having resumed C++ nationality for the last few months, I kind of miss D's auto
> keyword.
>> I am wondering, though, from an OO/polymorphism perspective, and UML and sound
> software engineering perspective as well, what does D's auto keyword buy you
> except (perhaps) laziness (in keystrokes)?
>> Sure the auto variable decl allows the declared var to take on the static type
> (i.e. as inferred by the compiler), but the programmer still has to know (in
> subsequent method invocations applied to the auto var) just what methods are valid
> for the statically inferred var type being the subject of the auto decl.
>> In some ways, as I said above, I miss "D auto" in C++; but then again, when I
> explicitly write the exact same type as the function return signature says, I feel
> more in control of my software design.
>> In an ideal world, which in of course such utopia does not really exist,  a pure
> OO model may well be that of single inheritance, and therefore all methods would,
> or could, be forced into a base class and hence, for object/polymorphic types
> D'auto keyword would not prove much advantage.
>> (Pray, let's not get into fragile base class discussions.)
>> At the end of the day, I'm not sure if D's auto keyword really helps to make my
> code more readable to others (alla programming-in-the-large) or if it just helps
> me with typing shortcuts (alla programming-in-the-small).
>> btw. 20 years ago I thought the Forth language was fantastic.  Then later I
> learned the difference between programming-in-the-small and programming-in-the-large.
>> Of course, Forth still hold fond memories for me .. but today I'd still rather
> stick to C++.
>> In writing this NG post, I was wondering about a subject line like "what's the
> best thing about D", but then my love/hate relationship with D's auto keyword
> really got me.
>> btw. Do any other languages have an "auto" var idiom?  I don't remember Scala
> having such (and it's really modern), though perhaps my memory lapses.
>> Cheers again,
>> Justin Johansson
>
> One underappreciated thing auto gives is DRY for types.  It makes it easier to
> change the type of some object in the place where it's initially decided, because
> those changes will automagically be propagated to everything that uses that
> object, as long as the new type supports the same compile-time interface as the
> old type.
This!

Makes some refactoring tasks ridiculously smooth.