On 01/13/2010 05:49 PM, Justin Johansson wrote:
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)?
A lot:
auto foo = bar(2);
auto baz = grok(foo);
No types to be seen here (aside from the literal 2) so you can:
1. rename the type whatever bar() returns without ripple effects through
this code
2. substitute the type itself for another type that obeys the same
structural interface.
In a way, it's like not using magic numbers only applied to types :) The
benefits are not limited too but more pronounced in templated code.
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.
Depends on how this is used I think, see also below.
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
All ML derived languages do this much more extensively and they even
don't need an auto keyword for it. C# has var and VB.NET has Dim which
mean the same thing. The nice thing with those languages is that if you
code in Visual Studio, you only have to hover above the variabele and
the type pops up. Most IDE's have this btw, including descent, so that
takes away the concern of having to remember the flow of types inferred.
