I see this recommended in the dart style guide, and copied in tons of tutorials and flutter source.
final foo = config.foo;
I don't understand it, how is this considered best practice when the readability is so poor? I have no clue what foo is here, surely final String foo = config.foo is preferable if we really want to use final?
This seems the equivalent to using var, which many consider a bad practice because it prevents the compiler from spotting errors and is less readable.
Where am I wrong?
In a lot of cases is does not really matter what type you are using as long the specific type can be statically determined by the compiler. When you are using var/final in Dart it is not that Dart does not know the type, it will just figure it out automatically based on the context. But the type must still be defined when the program are compiled so the types will never be dynamic based on runtime behavior. If you want truly dynamic types, you can use the dynamic keyword where you tell Dart "trust me, I know what I am doing with this types".
So types should still be defined where it matter most. This is e.g. for return and argument types for methods and class variables. The common factor for this types is that they are used to define the interface for using the method or class.
But when you are writing code inside a method, you are often not that interested in the specific types of variables used inside the method. Instead the focus should be the logic itself and you can often make it even more clear by using good describing variable names. As long the Dart analyzer can figure out the type, you will get autocomplete from your IDE and you can even still see the specific type from your IDE by e.g. Ctrl+Q in IntelliJ on the variable if you ends up in a situation where you want to know the type.
This is in particular the case when we are talking about the use of generics where it can be really tiresome to write the full specific type. Especially if you are using multiple generics inside each other like e.g. Map<String, List<String>>.
In my experience, Dart is really good to figure out very specific types and will complain loudly if your code cannot be determined statically. In the coming future, Dart will introduce non-null by default, which will make the Dart compiler and analyzer even more powerful since it will make sure your variable cannot be null unless this is something you specifically want and will make sure you are going to test for null when using methods which are specified to not expecting null.
About "Where am I wrong?". Well, a lot of languages have similar feature of var/final like Dart with the same design principle about the type should still be statically determined by a compiler or runtime. And even Java has introducing this feature. As a experienced Java and Dart programmer I have come to the conclusion for myself that typing inside methods are really not that important in a lot of cases as long I can still easily figure out the specific type by using an IDE when it really matters.
But it does make it more important to name your variables so they are clearly defining the purpose. But I am hoping you already are doing that. :)
I'm making a method inside a Ruby on Rails app called "print" that can take any string and converts it into a png. I've been told it's not good to make class methods for base ruby classes like String or Array or Hash, etc. so "some string to print".print is probably not something I should do.
I was thinking about making a subclass of String called Print (class Print < String) and storing it in my lib/assets folder. So it would look like: Print.new("some string to print"). So my question is, am I on the right track by 1) creating a sub-class from String and 2) storing it in lib/assets?
Any guidance would be greatly appreciated!
Answers to your question will necessarily be subjective because there are always be many answers to "where should I put functionality?", according to preference, principle, habit, customs, etc. I'll list a few and describe them, maybe add some of my personal opinions, but you'll ultimately have to choose and accept the consequences.
Note: I'll commonly refer to the common degenerate case of "losing namespacing scope" or "as bad as having global methods".
Monkeypatch/Extend String
Convenient and very "OO-message-passing" style at the cost of globally affecting all String in your application. That cost can be large because doing so breaks an implicit boundary between Ruby core and your application and it also scatters a component of "your application" in an external place. The functionality will have global scope and at worst will unintentionally interact with other things it shouldn't.
Worthy mention: Ruby has a Refinements feature that allows you to do do "scoped monkeypatching".
Worthy mention 2: Ruby also lets you includes modules into existing classes, like String.class_eval { include MyCustomization } which is slightly better because it's easier to tell a customization has been made and where it was introduced: "foo".method(:custom_method).owner will reveal it. Normal Monkeypatching will make it as if the method was defined on String itself.
Utils Module
Commonly done in all programming languages, a Util module is simply a single namespace where class methods/static methods are dumped. This is always an option to avoid the global pollution, but if Util ends up getting used everywhere anyways and it gets filled to the brim with unrelated methods, then the value of namespacing is lost. Having a method in a Util module tends to signify not enough thought was put into organizing code, since without maintenance, at it's worst, it's not much better than having global methods.
Private Method
Suppose you only need it in one class -- then it's easy to just put it into one private method. What if you need it in many classes? Should you make it a private method in a base class? If the functionality is inherent to the class, something associated with the class's identity, then Yes. Used correctly, the fact that this message exists is made invisible to components outside of that class.
However, this has the same downfall as the Rails Helper module when used incorrectly. If the next added feature requires that functionality, you'll be tempted to add the new feature to the class in order to have access to it. In this way the class's scope grows over time, eventually becoming near-global in your application.
Helper Module
Many Rails devs would suggest to put almost all of these utility methods inside rails Helper modules. Helper modules are kind of in between Utils Module and Private Method options. Helpers are included and have access to private members like Private Methods, and they suggest independence like Utils Modules (but do not guarantee it). Because of these properties, they tend to end up appearing everywhere, losing namespacing, and they end up accessing each other's private members, losing independence. This means it's more powerful, but can easily become much worse than either free-standing class/static methods or private methods.
Create a Class
If all the cases above degenerate into a "global scope", what if we forcibly create a new, smaller scope by way of a new class? The new class's purpose will be only to take data in and transform it on request on the way out. This is the common wisdom of "creating many, small classes", as small classes will have smaller scopes and will be easier to handle.
Unfortunately, taking this strategy too far will result in having too many tiny components, each of which do almost nothing useful by themselves. You avoid the ball of mud, but you end up with a chunky soup where every tiny thing is connected to every other tiny thing. It's just as complicated as having global methods all interconnected with each other, and you're not much better off.
Meta-Option: Refactor
Given the options above all have the same degenerate case, you may think there's no hope and everything will always eventually become horribly global -- Not True! It's important to understand they all degenerate in different ways.
Perhaps functionality 1, 2, 3, 4... 20 as Util methods are a complete mess, but they work cohesively as functionality A.1 ~ A.20 within the single class A. Perhaps class B is a complete mess and works better broken apart into one Util method and two private methods in class C.
Your lofty goal as an engineer will be to organize your application in a configuration that avoids all these degenerate cases for every bit of functionality in the system, making the system as a whole only as complex as necessary.
My advice
I don't have full context of your domain, and you probably won't be able to communicate that easily in a SO question anyways, so I can't be certain what'll work best for you.
However, I'll point out that it's generally easier to combine things than it is to break them apart. I generally advise starting with class/static methods. Put it in Util and move it to a better namespace later (Printer?). Perhaps in the future you'll discover many of these individual methods frequently operate on the same inputs, passing the same data back and forth between them -- this may be a good candidate for a class. This is often easier than starting off with a class or inheriting other class and trying to break functionality apart, later.
I'm not sure if this is the right place to ask this, since it's not really a technical question but more a question of style and coding practices...
I've always ben a fan of using "const" to define variables that will not be changing throughout their lifetime, most especially when they are parameters to functions/methods. This probably stems from my history with C++, where objects could be passed by reference rather than by pointer, but you wanted to ensure that the original value wasn't accidentally altered, either by you or by someone else on your team who was working on the same code snippet.
When looking through the headers for both Objective-C in general and Cocos2d specifically, I've noticed that there is a noticeable lack of use of this item. Now, I'm not against developing code as quickly as possible, and leaving off constraints such as these leave the developer the option to modify values as their code develops and evolves, but there are some instances where I believe that this laxity does not belong.
For example, in Cocos2D/UIKit, the "UIFont fontWithName" method takes "(NSString *)" as the parameter for the font name: does this method really need to reserve the right to alter the original string that was passed in? I personally like to define constant strings as "const" items, and I don't like the necessity of casting these as non-"const" when calling these methods.
Enough proselytizing: My question - Is the direction now moving towards less well-defined interfaces and more towards "lazy references" (which I do not consider to be a derogative term)?
Thanks in advance for any feedback....
Const wouldn't mean anything for Objective C class pointers, because it would have to be overloaded in a very confusing way for Objective C types. This is because there's no way to mark a method as const, as there is in C++, so the compiler could never enforce it.
That said, at my old company, we did declare global string constants using something like:
NSString* const kMyCoolString = #"Hello, world!";
The point being that it at least couldn't be reassigned to something else.
The closest analog in Objective C/Cocoa/Foundation are mutable/immutable versions of data structures, which doesn't really help your case.
I'm currently working on a Rails project, and have found times where it's easiest to do
if object.class == Foo
...
else if object.class == Bar
...
else
...
I started doing this in views where I needed to display different objects in different ways, but have found myself using it in other places now, such as in functions that take objects as arguments. I'm not precisely sure why, but I feel like this is not good practice.
If it's not good practice, why so?
If it's totally fine, when are times that one might want to use this specifically?
Thanks!
Not sure why that works for you at all. When you need to test whether object is instance of class Foo you should use
object.is_a? Foo
But it's not a good practice in Ruby anyway. It'd much better to use polymorphism whenever it's possible. For example, if somewhere in the code you can have object of two different classes and you need to display them differently you can define display method in both classes. After that you can call object.display and object will be displayed using method defined in the corresponding class.
Advantage of that approach is that when you need to add support for the third class or a whole bunch of new classes all you'll need to do is define display method in every one of them. But nothing will change in places where you actually using this method.
It's better to express type specific behavior using subtyping.
Let the objects know how they are displays. Create a method Display() and pass all you need from outside as parameter. Let "Foo" know to display foo and "Bar" know how to display bar.
There are many articles on replacing conditionals with polymorphism.
It’s not a good idea for several reasons. One of them is duck typing – once you start explicitly checking for object class in the code, you can no longer simply pass an instance of a different class that conforms to a similar interface as the original object. This makes proxying, mocking and other common design tricks harder. (The point can be also generalized as breaking encapsulation. It can be argued that the object’s class is an implementation detail that you as a consumer should not be interested in. Broken encapsulation ≈ tight coupling ≈ pain.)
Another reason is extensibility. When you have a giant switch over the object type and want to add one more case, you have to alter the switch code. If this code is embedded in a library, for example, the library users can’t simply extend the library’s behaviour without altering the library code. Ideally all behaviour of an object should be a part of the object itself, so that you can add new behaviour just by adding more object types.
If you need to display different objects in a different way, can’t you simply make the drawing code a part of the object?
I've been a bad programmer because I am doing a copy and paste. An example is that everytime i connect to a database and retrieve a recordset, I will copy the previous code and edit, copy the code that sets the datagridview and edit. I am aware of the phrase code reuse, but I have not actually used it. How can i utilize code reuse so that I don't have to copy and paste the database code and the datagridview code.,
The essence of code reuse is to take a common operation and parameterize it so it can accept a variety of inputs.
Take humble printf, for example. Imagine if you did not have printf, and only had write, or something similar:
//convert theInt to a string and write it out.
char c[24];
itoa(theInt, c, 10);
puts(c);
Now this sucks to have to write every time, and is actually kind of buggy. So some smart programmer decided he was tired of this and wrote a better function, that in one fell swoop print stuff to stdout.
printf("%d", theInt);
You don't need to get as fancy as printf with it's variadic arguments and format string. Even just a simple routine such as:
void print_int(int theInt)
{
char c[24];
itoa(theInt, c, 10);
puts(c);
}
would do the trick nickely. This way, if you want to change print_int to always print to stderr you could update it to be:
void print_int(int theInt)
{
fprintf(stderr, "%d", theInt);
}
and all your integers would now magically be printed to standard error.
You could even then bundle that function and others you write up into a library, which is just a collection of code you can load in to your program.
Following the practice of code reuse is why you even have a database to connect to: someone created some code to store records on disk, reworked it until it was usable by others, and decided to call it a database.
Libraries do not magically appear. They are created by programmers to make their lives easier and to allow them to work faster.
Put the code into a routine and call the routine whenever you want that code to be executed.
Check out Martin Fowler's book on refactoring, or some of the numerous refactoring related internet resources (also on stackoverflow), to find out how you could improve code that has smells of duplication.
At first, create a library with reusable functions. They can be linked with different applications. It saves a lot of time and encourages reuse.
Also be sure the library is unit tested and documented. So it is very easy to find the right class/function/variable/constant.
Good rule of thumb is if you use same piece three times, and it's obviously possible to generalize it, than make it a procedure/function/library.
However, as I am getting older, and also more experienced as a professional developer, I am more inclined to see code reuse as not always the best idea, for two reasons:
It's difficult to anticipate future needs, so it's very hard to define APIs so you would really use them next time. It can cost you twice as much time - once you make it more general just so that second time you are going to rewrite it anyway. It seems to me that especially Java projects of late are prone to this, they seem to be always rewritten in the framework du jour, just to be more "easier to integrate" or whatever in the future.
In a larger organization (I am a member of one), if you have to rely on some external team (either in-house or 3rd party), you can have a problem. Your future then depends on their funding and their resources. So it can be a big burden to use foreign code or library. In a similar fashion, if you share a piece of code to some other team, they can then expect that you will maintain it.
Note however, these are more like business reasons, so in open source, it's almost invariably a good thing to be reusable.
to get code reuse you need to become a master of...
Giving things names that capture their essence. This is really really important
Making sure that it only does one thing. This is really comes back to the first point, if you can't name it by its essence, then often its doing too much.
Locating the thing somewhere logical. Again this comes back to being able to name things well and capturing its essence...
Grouping it with things that build on a central concept. Same as above, but said differntly :-)
The first thing to note is that by using copy-and-paste, you are reusing code - albeit not in the most efficient way.
You have recognised a situation where you have come up with a solution previously.
There are two main scopes that you need to be aware of when thinking about code reuse. Firstly, code reuse within a project and, secondly, code reuse between projects.
The fact that you have a piece of code that you can copy and paste within a project should be a cue that the piece of code that you're looking at is useful elsewhere. That is the time to make it into a function, and make it available within the project.
Ideally you should replace all occurrances of that code with your new function, so that it (a) reduces redundant code and (b) ensures that any bugs in that chunk of code only need to be fixed in one function instead of many.
The second scope, code reuse across projects, requires some more organisation to get the maximum benefit. This issue has been addressed in a couple of other SO questions eg. here and here.
A good start is to organise code that is likely to be reused across projects into source files that are as self-contained as possible. Minimise the amount of supporting, project specific, code that is required as this will make it easier to reuse entire files in a new project. This means minimising the use of project specific data-types, minimising the use project specific global variables, etc.
This may mean creating utility files that contain functions that you know are going to be useful in your environment. eg. Common database functions if you often develop projects that depend on databases.
I think the best way to answer your problem is that create a separate assembly for your important functions.. in this way you can create extension methods or modify the helper assemble itself.. think of this function..
ExportToExcel(List date, string filename)
this method can be use for your future excel export functions so why don't store it in your own helper assembly.. i this way you just add reference to these assemblies.
Depending on the size of the project can change the answer.
For a smaller project I would recommend setting up a DatabaseHelper class that does all your DB access. It would just be a wrapper around opening/closing connections and execution of the DB code. Then at a higher level you can just write the DBCommands that will be executed.
A similar technique could be used for a larger project, but would need some additional work, interfaces need to be added, DI, as well as abstracting out what you need to know about the database.
You might also try looking into ORM, DAAB, or over to the Patterns and Practices Group
As far as how to prevent the ole C&P? - Well as you write your code, you need to periodically review it, if you have similar blocks of code, that only vary by a parameter or two, that is always a good candidate for refactoring into its own method.
Now for my pseudo code example:
Function GetCustomer(ID) as Customer
Dim CMD as New DBCmd("SQL or Stored Proc")
CMD.Paramaters.Add("CustID",DBType,Length).Value = ID
Dim DHelper as New DatabaseHelper
DR = DHelper.GetReader(CMD)
Dim RtnCust as New Customer(Dx)
Return RtnCust
End Function
Class DataHelper
Public Function GetDataTable(cmd) as DataTable
Write the DB access code stuff here.
GetConnectionString
OpenConnection
Do DB Operation
Close Connection
End Function
Public Function GetDataReader(cmd) as DataReader
Public Function GetDataSet(cmd) as DataSet
... And So on ...
End Class
For the example you give, the appropriate solution is to write a function that takes as parameters whatever it is that you edit whenever you paste the block, then call that function with the appropriate data as parameters.
Try and get into the habit of using other people's functions and libraries.
You'll usually find that your particular problem has a well-tested, elegant solution.
Even if the solutions you find aren't a perfect fit, you'll probably gain a lot of insight into the problem by seeing how other people have tackled it.
I'll do this at two levels. First within a class or namespace, put that code piece that is reused in that scope in a separate method and make sure it is being called.
Second is something similar to the case that you are describing. That is a good candidate to be put in a library or a helper/utility class that can be reused more broadly.
It is important to evaluate everything that you are doing with an perspective whether it can be made available to others for reuse. This should be a fundamental approach to programming that most of us dont realize.
Note that anything that is to be reused needs to be documented in more detail. Its naming convention be distinct, all the parameters, return results and any constraints/limitations/pre-requisites that are needed should be clearly documented (in code or help files).
It depends somewhat on what programming language you're using. In most languages you can
Write a function, parameterize it to allow variations
Write a function object, with members to hold the varying data
Develop a hierarchy of (function object?) classes that implement even more complicated variations
In C++ you could also develop templates to generate the various functions or classes at compile time
Easy: whenever you catch yourself copy-pasting code, take it out immediately (i.e., don't do it after you've already CP'd code several times) into a new function.