I am using the Rascal library for accessing syntax trees that are produced by the Eclipse Java compiler (JDT.rsc).
I am trying to get a fix on how the abstract syntax tree works. One thing that eludes me is the "variableBinding". Imagine a very simple class MyClass with one method doNothing() containing one statement, a variable declaration myVar. The declaration of the string variable myVar is represented in the AST-snipped below.
Inside the #bindings annotation, under the variableBinding key, there is a list that represents the consecutive components of a path to the variable myVar. The last item represents the actual variable itself, which is represented by the Id constructor variable(str name, int id).
Question: What is the meaning of the id?
It certainly isn't unique, because when I duplicate the method doNothing() and name it doNothing2(), I find variable("doNothing",0) and variable("doNothing2",0) in the AST. What exactly does it identify?
...
variableDeclarationFragment(
"myVar",
none())[
#bindings=(
"typeBinding":entity([
package("java"),
package("lang"),
class("String")
]),
"variableBinding":entity([
class("MyClass"),
method(
"doNothing",
[],
entity([primitive(void())])),
variable("myVar",0) // Here it's 0, but
])
),
#javaType=entity([
package("java"),
package("lang"),
class("String")
]),
#location=|project://my-project/src/MyClass.java|(60,5,<4,15>,<4,19>)
]
...
This id field actually appears to be an identifier assigned internally by Eclipse. You can see the JavaDoc for the IVariableBinding interface here, which is the source of the id:
http://help.eclipse.org/indigo/topic/org.eclipse.jdt.doc.isv/reference/api/org/eclipse/jdt/core/dom/IVariableBinding.html#getVariableId()
Just click on the link for getVariableId() if it doesn't take you there, and instead just takes you to the page for the interface. This is the method called to get the id. From what I can tell, it isn't very useful and can probably safely be ignored in most cases.
Related
I need to implement an abstract class function, which own a an specific data type. But I need inside my logic layer to make the attribute which is going to be passed as a dynamic data type. But when i Pass it to the function, i am sure that its data type will be as needed. So, i type (product.value.pickedImages) as ListOf5) . But it does an Exception.
The Abstract Class Code Is:
Future<Either<FireStoreServerFailures, List<String>>> uploadProductImages(
{required ListOf5<File> images});
The Implementation Code Is:
Future<Option<List<String>>> _uploadImagesToFirestorage() async {
return await productRepo
.uploadProductImages(
images: (product.value.pickedImages) as ListOf5<File>) // Exception
}
The Exception Is:
The argument type 'ListOf5 < dynamic>' can't be assigned to the
parameter type 'ListOf5 < File>'.
You are trying to cast the List from List<dynamic> to List<String>.
Instead, you should cast each item, using something like this:
void main() {
List<dynamic> a = ['qwerty'];
print(List<String>.from(a));
}
Not sure about the implementation of this ListOf5 though...
The cast (product.value.pickedImages) as ListOf5<File> fails.
It fails because product.value.pickedImages is-not-a ListOf5<File>, but instead of ListOf5<dynamic> (which may or may not currently contain only File objects, but that's not what's being checked).
Unlike a language like Java, Dart retains the type arguments at run-time(it doesn't do "erasure"), so a ListOf5<dynamic> which contains only File objects is really different from a ListOf5<File> at run-time.
You need to convert the ListOf5<dynamic> to a ListOf5<File>.
How to do that depends on the type ListOf5, which I don't know.
For a normal List, the two most common options are:
(product.value.pickedImages).cast<File>(). Wraps the existing list and checks on each read that you really do read a File. It throws if you ever read a non-File from the original list. Perfectly fine if you'll only read the list once.
List<File>.of(product.value.pickedImages). Creates a new List<File> containing the values of product.value.pickedImages, and throws if any of the values are not File objects. Requires more memory (because it copies the list), but fails early in case there is a problem, and for small lists, the overhead is unlikely to be significant. If you read the resulting list many times, it'll probably be more efficient overall.
If the ListOf5 class provides similar options, you can use those. If not, you might have to build a new ListOf5 manually, casting each element of the existing ListOf5<dynamic> yourself.
(If the ListOf5 class is your own, you can choose to add such functionality to the class).
So the following code snippet
Set mySet = {1,2,3};
is an instance of type Set which is permissible, however what would the class of the set literal be. I have tried to search for this, however I have found no answer in the dart documentation.
A literal exists only in your source code. Asking for its "class" doesn't make a lot of sense.
Using a Set, Map, or List literal is just syntactic sugar for invoking a corresponding constructor. The Set factory constructor constructs a LinkedHashSet.
However, you'll see that LinkedHashSet is also abstract. Its factory constructor returns an instance of a private, internal class. You can see its typename via print(Set().runtimeType); the actual type might be different for different platforms and is unlikely to be useful to you.
What is wrong with my code?
widget.woList is this datatype List<HashMap<int, ABC>>()
for (var i in widget.woList) {
print(i.toString());
}
By printing above code, I get
{5838: ABC(pid: 84201,userId: 545)}
But when I want to get only key ( print(i.key.toString());), I get below error:
Class '_HashMap<int, ABC>' has no instance getter 'key'.
Receiver: Instance of '_HashMap<int, ABC>'
Tried calling: key
I think you need to loop through the HashMap as well:
for (HashMap<int, ABC> i in list) {
i.forEach((key, value) {
print(key.toString());
print(value.toString());
});
}
Make sure you typo the "i" variable in the for with HashMap<int, ABC> to get autocompletes from your IDE.
The analyzer should give an error in your case since a Map does not contain any property with the name key. Instead the name is keys which return a Iterable of keys in the map:
https://api.dart.dev/stable/2.8.1/dart-core/Map/keys.html
A map can contain multiple keys but if you know there are only one key in the map you can do something like: i.keys.first.toString(). But if there are multiple keys you need to loop through them.
I will recommend you use auto completion in your IDE when programming in Dart and make use of the analyzer. By using the tools the SDK provides, it is much easier to browse what properties and methods there are in each class together with the documentation. And since Dart can figure out the type of lots of variables automatically, you can use the IDE to also identify the type of each variable without even running the program.
I have been using XOM parser in a project that is mostly over. The parser is very good and I find it mostly stable. However today I was parsing an XML element with an attribute called "xml:lang"
The getAttributeValue("xml:lang") returned null instead of "English". I could find a work around to get the value by using getAttribute(int location).getValue()
However, it would be better to use the method getAttributeValue because the attribute's location changes for other elements.
I am not sure whether I am doing something wrong or a small bug lies there in the library method.
The xml:lang attribute is in a namespace.
To get the value of an attribute in a namespace, use the Element.getAttributeValue(String, String) method. The first parameter needs to be the local name of the attribute (after the colon), which is lang in this case. The second parameter needs to be the URI of the namespace, which is usually defined in an ancestor element. The xml namespace, however, is built in and always has the namespace URI http://www.w3.org/XML/1998/namespace.
Therefore, some code like this should do what you want (assuming you have a variable called element pointing to your element):
String lang = element.getAttributeValue("lang", "http://www.w3.org/XML/1998/namespace");
I've found properties corresponding to each action named like this: MVC.<Controller>.<Action>Params, they contain parameter names for each action. What are they for and how they can be used?
There were some edge scenarios where it was interesting to pass the parameter name as a constant. I can't instantly recall what that person was doing, but I could see this being useful is calls to AddRouteValue. In the end, it's all about never to have to use a literal string that refers to a C# object, whether it's a class, method, or param.