I would like to know if the following is possible in Scala (but I think the question can be applied also to Java):
Create a Scala file dynamically (ok, no problem here)
Compile it (I don't think this would be a real problem)
Load/Unload the new class dynamically
Aside from knowing if dynamic code loading/reloading is possible (it's possible in Java so I think it's feasible also in Scala) I would like also to know the implication of this in terms of performance degradation (I could have many many classes, with no name clash but really many of them!).
TIA!
P.S.: I know other questions about class loading in Scala exist, but I haven't been able to find an answer about performance!
Yes, everything you want to do is certainly possible. You might like to take a look at ScalaMock, which is an example of creating Scala source code dynamically. And at SBT which is an example of calling the compiler from code. And then there are many different systems that load classes dynamically - look at the documentation for loadLibrary as a starting point.
But, depending on what you want to achieve, you might like to look at Scala Macros instead. They provide the same kind of flexibility as you would get by generating source code and then compiling it, but without many of the downsides of that approach. The original version of ScalaMock used to work by generating source code, but I'm in the process of moving to using macros instead.
It's all possible in Scala, as is clearly demonstrated by the REPL. It's even going to be relatively easy with Scala 2.10.
i'm currently working on a big projekt and i loose many time searching the right thing in the code. i need to get e.g. a method which makes someting special. so i scroll the whole code.
are there any common and effective methods to struct a file of code? e.g.
1. all global variables
2. constructor etc.
3. all methods
4. all event handlers
do you know common methods to do this??
It's more usual to break large projects into several source files, with logically related functionality. This helps with speeding up compilation and reducing coupling in your design as well as helping you navigate the code.
An example might be to have separate files for
UI functionality
helper classes (such as geometric/maths stuff)
file I/O
core functionality that connects the rest together
Design is a large topic, the book Code Complete by Steve McConnell might be a good starting point for you.
You shouldnt use global variables :)
Try spreading things out over different classes and files. Maks sure each class has only one purpose, instead of 1 class that manages a whole lot of different tasks.
That sounds like a sensible enough structure to me, what would really benefit you though is learning to use the tools you have available — whatever editor you're using it will have a search function, you can use that to quickly find what you're looking for.
Some editors will also include bookmarks too, and most offer a way to move back and forward through recent positions in the file.
Seen this sort of things started, never seen it kept on under the pressure to turn out code though.
Basically my rule of thumb is, if I feel the need to do this, break the code file up.
For example, referencing something as System.Data.Datagrid as opposed to just Datagrid. Please provide examples and explanation. Thanks.
The benefit is that you don't need to add an import for everything you use, especially if it's the only thing you use from a particular namespace, it also prevents collisions.
The downside, of course, is that the code balloons out in size and gets harder to read the more you use specific qualifiers.
Personally I tend to use imports for most things unless I know for sure I will only be using something from a particular namespace once or twice, so it won't impact the readability of my code.
You're being very explicit about the type you're referencing, and that is a benefit. Although, in the very same process you're giving up code clarity, which clearly is a downside in my case, as I want code to be readable and understandable. I go for the short version unless I have a conflict in different namespaces which can only be solved with the explicit referencing to classes.. Unless I make an alias for it with the keyword using:
using Datagrid = System.Data.Datagrid;
Actually the full path is global::System.Data.DataGrid. The point of using a more qualified path is to avoid having to use additional using statements, especially if the introduction of another using will cause problems with type resolution. More fully qualified identifiers exist so that you can be explicit when you need to be explicit, but if the class's namespace is clear, then the DataGrid version is clearer to many.
I generally use the shortest form available in order to keep the code as clean and readable as possible. That's what using directives are for, after all, and tooltips in the VS editor give you instant detail on the provenance of a type.
I also tend to use a namespace tag for RCWs in a COM interop layer, to call out those variables explicitly in the code (they may need special attention on lifecycle and collection), eg
using _Interop = Some.Interop.Namespace;
In terms of performance there is no upside/downside. Everything is resolved at compile time and the generated MSIL is identical whether you use fully-qualified names or not.
The reason why its use is prevalent in the .NET world is because of auto-generated code, such as designer markup. In that case it would be better to fully-qualify names like class names because of possible conflicts with other classes you may have in your code.
If you have a tool like ReSharper, it will actually tell you what fully-qualified references you have are unnecessary (e.g. by graying them out) so you can lop them off. If you frequently cut-paste code across your various code bases, it would be a must to fully qualify them. (then again, why would you want to do cut-paste all the time; it's a bad form of code reuse!)
I don't think there is really a downside, just readability vs actual time spent coding. In general if you don't have namespaces with ambiguous object I don't think it's really needed. Another thing to consider is level of use. If you have one method that uses reflection and you are alright with typeing System.Reflection 10 times, then it's not a big deal but if you plan on using a namespace alot then I would recommend an include.
Depending on your situation, extra qualifiers will generate a warning (if this is what you mean by redundant). If you then treat warnings as errors, that's a pretty serious downside.
I've run into this with GCC for example.
struct A {
int A::b; // warning!
}
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For those of you in the Visual Studio environment, how do you feel about wrapping any of your code in #regions? (or if any other IDE has something similar...)
9 out of 10 times, code folding means that you have failed to use the SoC principle for what its worth.
I more or less feel the same thing about partial classes. If you have a piece of code you think is too big you need to chop it up in manageable (and reusable) parts, not hide or split it up.It will bite you the next time someone needs to change it, and cannot see the logic hidden in a 250 line monster of a method.
Whenever you can, pull some code out of the main class, and into a helper or factory class.
foreach (var item in Items)
{
//.. 100 lines of validation and data logic..
}
is not as readable as
foreach (var item in Items)
{
if (ValidatorClass.Validate(item))
RepositoryClass.Update(item);
}
My $0.02 anyways.
This was talked about on Coding Horror.
My personal belief is that is that they are useful, but like anything in excess can be too much.
I use it to order my code blocks into:
Enumerations
Declarations
Constructors
Methods
Event Handlers
Properties
Sometimes you might find yourself working on a team where #regions are encouraged or required. If you're like me and you can't stand messing around with folded code you can turn off outlining for C#:
Options -> Text Editor -> C# -> Advanced Tab
Uncheck "Enter outlining mode when files open"
I use #Region to hide ugly and useless automatically generated code, which really belongs in the automatically generated part of the partial class. But, when working with old projects or upgraded projects, you don't always have that luxury.
As for other types of folding, I fold Functions all the time. If you name the function well, you will never have to look inside unless you're testing something or (re-)writing it.
While I understand the problem that Jeff, et. al. have with regions, what I don't understand is why hitting CTRL+M,CTRL+L to expand all regions in a file is so difficult to deal with.
I use Textmate (Mac only) which has Code folding and I find it really useful for folding functions, I know what my "getGet" function does, I don't need it taking up 10 lines of oh so valuable screen space.
I never use it to hide a for loop, if statement or similar unless showing the code to someone else where I will hide code they have seen to avoid showing the same code twice.
I prefer partial classes as opposed to regions.
Extensive use of regions by others also give me the impression that someone, somewhere, is violating the Single Responsibility Principle and is trying to do too many things with one object.
#Tom
Partial classes are provided so that you can separate tool auto-generated code from any customisations you may need to make after the code gen has done its bit. This means your code stays intact after you re-run the codegen and doesn't get overwritten. This is a good thing.
I'm not a fan of partial classes - I try to develop my classes such that each class has a very clear, single issue for which it's responsible. To that end, I don't believe that something with a clear responsibility should be split across multiple files. That's why I don't like partial classes.
With that said, I'm on the fence about regions. For the most part, I don't use them; however, I work with code every day that includes regions - some people go really heavy on them (folding up private methods into a region and then each method folded into its own region), and some people go light on them (folding up enums, folding up attributes, etc). My general rule of thumb, as of now, is that I only put code in regions if (a) the data is likely to remain static or will not be touched very often (like enums), or (b) if there are methods that are implemented out of necessity because of subclassing or abstract method implementation, but, again, won't be touched very often.
Regions must never be used inside methods. They may be used to group methods but this must be handled with extreme caution so that the reader of the code does not go insane. There is no point in folding methods by their modifiers. But sometimes folding may increase readability. For e.g. grouping some methods that you use for working around some issues when using an external library and you won't want to visit too often may be helpful. But the coder must always seek for solutions like wrapping the library with appropriate classes in this particular example. When all else fails, use folding for improving readibility.
This is just one of those silly discussions that lead to nowhere. If you like regions, use them. If you don't, configure your editor to turn them off. There, everybody is happy.
I generally find that when dealing with code like Events in C# where there's about 10 lines of code that are actually just part of an event declaration (the EventArgs class the delegate declaration and the event declaration) Putting a region around them and then folding them out of the way makes it a little more readable.
Region folding would be fine if I didn't have to manually maintain region groupings based on features of my code that are intrinsic to the language. For example, the compiler already knows it's a constructor. The IDE's code model already knows it's a constructor. But if I want to see a view of the code where the constructors are grouped together, for some reason I have to restate the fact that these things are constructors, by physically placing them together and then putting a group around them. The same goes for any other way of slicing up a class/struct/interface. What if I change my mind and want to see the public/protected/private stuff separated out into groups first, and then grouped by member kind?
Using regions to mark out public properties (for example) is as bad as entering a redundant comment that adds nothing to what is already discernible from the code itself.
Anyway, to avoid having to use regions for that purpose, I wrote a free, open source Visual Studio 2008 IDE add-in called Ora. It provides a grouped view automatically, making it far less necessary to maintain physical grouping or to use regions. You may find it useful.
I think that it's a useful tool, when used properly. In many cases, I feel that methods and enumerations and other things that are often folded should be little black boxes. Unless you must look at them for some reason, their contents don't matter and should be as hidden as possible. However, I never fold private methods, comments, or inner classes. Methods and enums are really the only things I fold.
My approach is similar to a few others here, using regions to organize code blocks into constructors, properties, events, etc.
There's an excellent set of VS.NET macros by Roland Weigelt available from his blog entry, Better Keyboard Support for #region ... #endregion. I've been using these for years, mapping ctrl+. to collapse the current region and ctrl++ to expand it. Find that it works a lot better that the default VS.NET functionality which folds/unfolds everything.
I personally use #Regions all the time. I find that it helps me to keep things like properties, declarations, etc separated from each other.
This is probably a good answer, too!
Coding Horror
Edit: Dang, Pat beat me to this!
The Coding Horror article actual got me thinking about this as well.
Generally, I large classes I will put a region around the member variables, constants, and properties to reduce the amount of text I have to scroll through and leave everything else outside of a region. On forms I will generally group things into "member variables, constants, and properties", form functions, and event handlers. Once again, this is more so I don't have to scroll through a lot of text when I just want to review some event handlers.
I prefer #regions myself, but an old coworker couldn't stand to have things hidden. I understood his point once I worked on a page with 7 #regions, at least 3 of which had been auto-generated and had the same name, but in general I think they're a useful way of splitting things up and keeping everything less cluttered.
I really don't have a problem with using #region to organize code. Personally, I'll usually setup different regions for things like properties, event handlers, and public/private methods.
Eclipse does some of this in Java (or PHP with plugins) on its own. Allows you to fold functions and such. I tend to like it. If I know what a function does and I am not working on it, I dont need to look at it.
Emacs has a folding minor mode, but I only fire it up occasionally. Mostly when I'm working on some monstrosity inherited from another physicist who evidently had less instruction or took less care about his/her coding practices.
Using regions (or otherwise folding code) should have nothing to do with code smells (or hiding them) or any other idea of hiding code you don't want people to "easily" see.
Regions and code folding is really all about providing a way to easily group sections of code that can be collapsed/folded/hidden to minimize the amount of extraneous "noise" around what you are currently working on. If you set things up correctly (meaning actually name your regions something useful, like the name of the method contained) then you can collapse everything except for the function you are currently editing and still maintain some level of context without having to actually see the other code lines.
There probably should be some best practice type guidelines around these ideas, but I use regions extensively to provide a standard structure to my code files (I group events, class-wide fields, private properties/methods, public properties/methods). Each method or property also has a region, where the region name is the method/property name. If I have a bunch of overloaded methods, the region name is the full signature and then that entire group is wrapped in a region that is just the function name.
I personally hate regions. The only code that should be in regions in my opinion is generated code.
When I open file I always start with Ctrl+M+O. This folds to method level. When you have regions you see nothing but region names.
Before checking in I group methods/fields logically so that it looks ok after Ctrl+M+O.
If you need regions you have to much lines in your class. I also find that this is very common.
region ThisLooksLikeWellOrganizedCodeBecauseIUseRegions
// total garbage, no structure here
endregion
Enumerations
Properties
.ctors
Methods
Event Handlers
That's all I use regions for. I had no idea you could use them inside of methods.
Sounds like a terrible idea :)