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In computer programming with object-oriented programming languages, duck typing is a style of typing in which an object's methods and properties determine the valid semantics, rather than its inheritance from a particular class or implementation of a specific interface.
An interesting read, but something remains unclear to me: Why would you want to have something like
It's seams that he try to invent a kind of environment where the compiler/linker/runtime will decide - based on actual structure - if types are equal or not. I can image how much fun it should be when two types render incompatible because you added some property to one of them...
I remember working on a VB6 project - okay, I know - and we used duck typing to get around a lot of problems with inheritance in the language. The object relationships were mostly loose and most cross calls were based on config. It worked and it was useful, however when it came to managing the method signatures fun ensued.
Check out the article that the OP linked - it's Eric Lippert (a long time C# compiler writer until he recently left MS) specifically linking to that Wikipedia article and picking apart what it says about Duck Typing.
He even specifically derides that C# dynamic explanation you noted offered by that article.
template <class T> class Foo: public T
int Baa(int k)
T * pT = static_cast<T*>(this); // this is the magicreturn42 + pT->Baz(k - 3); // for instance.
Any class that exposes a method Baz that returns something that can be converted to an integer, and can be called with an integer parameter, can be a template paremeter for class Foo. No special interfaces required, so it is less restrictive than, for instance, C# generics. Aside: 'less restrictive' doesn't mean 'better', or 'worse'. Also, the code above is resolved at compile time, which may have a noticeable impact on performance.
"Accident: An inevitable occurrence due to the action of immutable natural laws." (Ambrose Bierce, circa 1899). "You are to act in the light of experience as guided by intelligence" (Rex Stout, "In the Best Families", 1950).
Ah yes, the Curiously Reoccuring Template Pattern reoccurs....
Templates are highly infectious, suddenly everything working with this type(s) has to be a template over that type. Templates still affect the tool chain significantly, and have some problems with other features (such as static data).
There is no explicit statement what T needs to support. Foo<T> can be instantiated for any struct / class typetype:
In a real app you can expect a dozen of "cool candidates", some that work and some you wish they did and that Baa() call ist hidden in deep jungle of calls, throwing error messages about a dozen of templated types you never heard of.
Duck Typing (or C++ concepts) would allow to reject early, at the instantiation of Foo<cool>.
C# has been internally using duct typing for a very long time.
For example, the C#’s foreach operator already uses duck typing. This might be surprising to some, but to support foreach in C# you don’t need to implement IEnumerable! All you have to do is:
Provide a public method GetEnumerator that takes no parameters and returns a type that has two members: a) a method MoveMext that takes no parameters and return a Boolean, and b) a property Current with a getter that returns an Object.
I think in a statically-typed language, Duck Typing would subvert all of the strengths of that environment. Indeed, Interfaces provide all of the function offered by Duck Typing, with the additional benefit of compile-time type checking.
Duck Typing, to me, is more of an approach or way of thinking than an actual type system. In dynamic languages, with no compile-time checks, thinking in terms of "duck typing" can be a tool for designing code structure.
In most cases, IMHO, if we work in a static language and think "duck typing" we should immediately think "interface" instead.
SO I go to change the thrmostat on the alfa 156 JTS Veloce yadda yadda yadda super duper jobby, because its running at 50C, and the bottom bolt shears off in the cylinder head.
Its an 8.8 carbon steel bolt too, so its going to be a pig to drill and easy out, and I gont have a MIG welder to weld a nut to whats left (this actually works well since so much heat is rammed into the bolt that it frees itself). And the angle to drill is not perfect, so there is little chance of drilling straight down the thing, even with the battery out, and I dont want to have to take the head off.
So, plan 2, put a couple of holes in either side of the sheared off bolt, drill to 6.8, tap to M8 x 1.25, and stick in some M8 stud. Then make up a little plate with two holes to fit over the studs, and pull the thermostat flange up tight. Should do it. Just need to find some place to get the right drill size...
Still, changed the lamnda sensor, did an oil change, and found the knock, the front right suspension turret was lose.
Tell you what, Italian stuff isnt as good as it was. There is no way they would use a steel bolt in an ally head in the old days, a bit of stud and a nut is far better; the stud corrodes to the ally, and the nut would always undo. Thats how they used to make their engines, what wrong with the twats?
They dont rust anymore, and the electrics seem to be relatively OK so its a reasonable car to have today. I replaced a BMW 316 coupe with it, a 156 JTS Veloice, and have to say the BMW feels agricultural in comparison, yes, it has very good grip, but almost no feel compared to the Alfa. I have often had this impression with German cars, utterly dead feeling.
Whats the SZ, a 2 liter, 1750? The engine looks exactly the same as tihe one on my GTV
I used to have one, its a super tough engine, and really well made. For example the exhaust valve stems are hollow wnd half filled with sodium. When the engine gets hot, the sodiujm melts and sloshes back and forward carrying heat away from the valve head. Do you know ANY other car manufacturer that goes to such detail opn their engines? Just nuts, but thats Alfa for you (and Fiat to a large degree).
It will be easy to work on, and fun to maintain,m as well as a joy to take out for a blast when the weathers good. And the thing with alfas/fiats, you can really drive them hard, they love it, and are made for it.
I need to change the cam belt too, probelem is you are supposed to use special tools, not that I ever did on any of the other Fiats I changed belts on before.
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