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Such a FoodDto is absolutely useless, a snapshot in time...
There is little point in deriving from it...
This FooDto sole purpose is to be turned into json and vice versa. It comes from an object that do update each individual property in real time (mostly hardware read status)
would be nice...
unfortunately the way the DLL dependency tree is set... can't happen...
i.e. the FooClass is in a DLL that reference the assembly where FooDto is defined....
FooDto is in a common contract assembly...
Nobody seems to have yet mentioned any other alternatives...one would be passing in a structure with 24 members as an initializer, although in C# that doesn't really eliminate the problem, since you'd have a similar problem with how to initialize the structure. Might be useful tho if you instantiated a lot of these objects with mostly the same parameters.
I would never condone instantiating a class without initializing all member data items, but if there are reasonable default values for them, I could see an initializer (or maybe even a few) that initialized all or most of them to default values, and only set one or two to non-default values. Don't ever want to leave values uninitialized, however.
Of course, there are those who would say that any object that needs this many initializers is poorly designed and should be refactored. It would be up to the author in each individual case to decide if this is feasible.
For my money, this makes a good case for a language feature I've been wanting ever since the days I worked with the ADA language - named parameter lists. Then you could offer default values for all parameters, and let the caller set only the ones (s)he wants to differ from the default values. Of course, you can emulate this now in C#, but it requires 2^n constructors. I've done it with three parameters (eight constructors), but of course it would be impractical with 24.
Putting all of those properties as separate parameters of a method is something I was forced to do by someone who got his code from a glorious "whitepaper", and has resulted in hours added on to debugging when one of the parameters is wrong in some way, and has resulted in unnecessarily lengthy code calling those methods for every property even when only one or two properties need to be set.
You could propose an option 3, that has an object with all the items that need to be passed in. According to Martin Fowler, too many options passed into a constructor is a code smell.
A large list of construction parameters, like any large parameter list, is a CodeSmell. Usually when I see these I find that many of the parameters are DataClumps and should be replaced by their own object. Having said that it's not unusual for constructor methods to have more parameters than other methods - but they are a good place to spot data clumps.
I believe there are reasons for either style and I don't mean a simple preference by the developer.
The first style allows you to initialise an object with some default values and gradually fill its properties with desired non-default values. Also it allows you to change those values over time to reflect changes in how the class (or another dependent class) should behave. You can see that in any visual component for UWP/WPF/ASP.NET. Meanwhile, the second style creates a kind of immutable object (it can only be read although its properties can still be changed due to internal operations, if any). Changes to this data may not be desired due to e.g. the intended design of the application (or API) or legal reasons.
If you must follow the second style with a class with so many constructor arguments (with which I agree it might be a code smell), I'd recommend creating a Builder for the object. MyFooClass in this example seems to be one which might actually hint at why the guy wanted you to change the code style; perhaps he thought you were trying to create in MyFooClass a Builder for FooDto and wanted you to make it so both classes don't repeat themselves. Anyway, I'd recommend approaching the guy with an open mind to try and understand his motivations for requesting the style change; it may either enhance your knowledge of the application or the guy you're working with.
[UPDATED] Both Dan's or Marc's answers offer a great alternative to avoiding so many arguments on the constructor. I'd also check if you could go either way.
I personally don't like either option. Why create two classes that duplicate the same information. I would create a property in MyFooClass to point to FooDto. Or better yet, inherent MyFooClass from FooDto.
FooDto could be final for all we care. its whole intent, purpose, life cycle, is to turn Data into JSON and vice versa. Nothing more....
mm.. I'd like the idea of justsharing my own internal status class... but that won't fly either.. plus I have been forced to take in some dependency that prevent having these internal status in shared library.. So I do need to duplicate them in contract library upon which I depend
There should never be a possibility where an object can get constructed without it being initialized properly. Making them mandatory or optional parameters to a constructor achieves that, and the compiler will find every last place where someone has initialized the object incorrectly. Not only that, it'll run very early in the development process, ensuring that the developer that just added the new parameter has all those details still fresh in their head when the bugs are found. What better unit test could you possibly hope for?
The other aspect of how you've been asked to rewrite that code is also a better practice -- you've been asked to reduce the public interface by removing the property setters. This just ensures that nobody can reach into your object and twiddle those properties after it's been constructed. If someone needs that, they can change your code, but hopefully they will evaluate whether there's a better that ensures the object can't be put in a bad state. If the object can't ever be put in a bad state, you can't have bugs because someone was sloppy.
In a recent survey, 2/3 of the lions said that they were happy to serve as King of the Forest, while another 1/9 thought it was way too much responsibility. If 14 lions gave one of these two answers, how many lions were surveyed in total?
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