I am using AADL which is domain specific language created using Xtext and EMF. I am trying to use function IResourceServiceProvider.Registry.INSTANCE.getResourceServiceProvider(URI.createFileURI("dummy.aadl")) but it returns null. how can I fix it?
It looks like you did never called the doSetup method of the AADLStandalibeSetup (or however your language impl is called). It is used to register your language if you do not run in an OSGi equinox environment.
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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 currently working on a library, and ran into some strange inconsistencies in behaviour between my unit test code, and an actual app I'm basing on the code.
See, I'm trying to get a Type struct from the name of the class I want to instantiate, but I get nothing (e.g. Type is there, but name() produces null, is_a() fails, etc.)
However, if I make an instance of the type first, then try to get the Type based on name once more, it works just as I expected (which is probably why my unit tests work)
So I was wondering, when is a type registered by the type system and available via. from_name(...) ?
Does the type system only know it after it has been instantiated at run time? Is there another reason a class name wouldn't be recognized until an instance of the class has been instantiated? Should I use some other method of registration?
I'm coding in Vala if that makes any kind of a difference.
A type is first registered with the type system when its get_type() function is called. This is called in a number of places, basically whenever you need to get the GType for that type. Typically, it will first be called during class_init of the type, which happens during the first instance init.
So essentially you are right when you say “does the type system only know it after it has been instantiated at run time”, because that’s normally what happens. However, you can bring type registration forward by explicitly calling the get_type() function for a type early, and passing it to g_type_ensure(). For example, see what GLib does here:
/* Initialize types from built-in "modules" */
g_type_ensure (g_null_settings_backend_get_type ());
g_type_ensure (g_memory_settings_backend_get_type ());
g_type_ensure (g_keyfile_settings_backend_get_type ());
…
I have a union type that has a single, empty case.
type Default =
| Default
This type has a purpose, but it's not meant to be visible or usable.
Unfortunately, I have to use it in an inline function that does need to be visible. This prevents me from making the type or the case private.
The solution I came up with is using the CompilerMessageAttribute on it to signal an error whenever it's used. This would be fine, but now I can't compile my own assembly because IT uses it.
Is there a way to signal an error only when it's used by an assembly that references my assembly?
Let me reiterate the requirements to make sure I understand them:
The type needs to be public, so that that other assemblies can reference it implicitly via inline.
But if other assemblies reference it explicitly, then that is an error.
I don't know of any way of doing this using standard tooling.
I can see two possible solutions.
If only one calling assembly needs to use the inline function, what about making the type internal and then have the calling assembly be a friend assembly, using the InternalsVisibleToAttribute.
The only other alternative I can think of is security by obscurity. Hide the type in some awkwardly named module and require module qualification. This will stop accidental use of the type, if nothing else.
You could even add a build step to check that no source code references the module name.
[<RequireQualifiedAccessAttribute>]
module ``Dont Use This`` =
type Default =
| Default
let x = ``Dont Use This``.Default
And yes, it's very kludgy.
I'm currently working on a project with symfony 1.4 and Doctrine 1.2. I'm looking for a proper way to do logging from the model layer.
In some model classes I use the record hook postSave() to create a ZIP file using exec() (since PHP zip doesn't provide for storage method 'Stored'). To be sure that everythings works fine I check the return code and log an error if something goes wrong. My first naive approach was to do it like this:
if ($returnCode != 0) {
sfContext::getInstance()->getLogger()->debug(...);
}
As you know, this doesn't work so well because sfContext belongs to the controller layer and shouldn't be used from the model layer. My next try was to use the model's constructor to pass in an sfLogger instance, but this doesn't work due to Doctrine 1.2 reserving the constructor for internal use (Doctrine 1.2 Documentation).
I'm looking forward for your suggestions!
You can add a setLogger() method to your function, that gets a logger instance in a parameter, and sets it to an internal variable, like $this->logger. Later, when you need to log something, do it like if ($this->logger) { $this->logger->debug(...); }.
im calling an actionscript class from my main mxml file. the actionscript class is responsible for calling a web service and handling the response, however im having trouble and keep getting the following error; (im new to flex btw)
Error #1009: Cannot access a property or method of a null object reference.
my code goes as follows;
public function getSites(argWsdl:String):void{
ws = new WebService();
ws.loadWSDL(argWsdl);
ws.getSites.addEventListener(ResultEvent.RESULT,echoResultHandler);
ws.getSites();
}
public function echoResultHandler(event:ResultEvent):void {
var siteField:ArrayCollection = event.result as ArrayCollection;
Application.application.setSiteField(siteField);
}
when i run the debugger the code never reaches the result hanlder and i see the #1009 error in the variable list.
any ideas?
looks like you have it sorted, but just to add more information in case someone else comes along to this question, you generally see this error when you are trying to use something that hasn't been created yet. A lot of the time you will see it when trying to access UI components that have not yet been created (its good to rely on the creationComplete event for these sort of things), but in this case it looks like you are using the webservice before it is completely ready (the wsdl hasnt been loaded yet).
Just so you know, you can also define your webservices in mxml (mx:webservice) and specify the wsdl there or you can also load the wsdl later on from a configuration file afterwards just by referencing the ID.
sorted it out,
i needed to created a loadEvent and loadhandler. Once loadWsdl is called the loadhandler specifies the laodHandler to use, inside the loadHandler i call the method name as seen in the wsdl
thanks Ryan,
the main reason im using a seperate actionscript class is so i can reuse the same web service calls across my components without having to retype the same code. I couldnt think of a better way to do this - maybe a could have done the same with a custom component