I have a proxy object which uses noSuchMethod to relay invocations to other objects, but the proxy object exists in a minified/obfuscated environment, and the objects it relays the invocations to are in a non-minified/obfuscated state, so when the name of the method being called reaches the non-minified environment the names don't match up, I have the myFile.dart.js.map file, is there a simple algorithm to parse this and get the original invocation name back from the minified name using the source maps? or even better is there a library that already does this in dart?
You can use MirrorSystem.getName to get the real name of a symbol. In the case of noSuchMethod :
noSuchMethod(Invocation invocation) {
String member = MirrorSystem.getName(invocation.memberName);
}
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).
C# discards prevent allocation of values not needed. Is there something similar in dart? I saw a lot of people use the underscore as if it were a discard, but using two at the same time (like this (_, _) => method() will say the variable _ is already defined.
Dart does allow you to use the same discard operator as C#. You can define a variable or final with a name of _. This works well with the rule avoid-ignoring-return-values (Dart Code Metrics) Importantly, if you name the variable with this, you will not encounter the warning unused-local-variable. However, there is another code rule called no_leading_underscores_for_local_identifiers. You can safely turn this off as long as you don't have someone in your team that has a habit of prefixing variable names with an underscore.
Ignoring the return value
Discarding the return variable
Unfortunately, it doesn't work the same way as C# because it involves an assignment, and you cannot assign two different types to it. You need to declare it as an Object?
I am trying to call a method of a class that I only know by name as a String. Now therefore I would need a ClassMirror of that class that allowes me to instantiate an instance. However, creating ClassMirrors seems to be only possible by entering a type using reflectClass(Type) or by passing an already existing instance of that class into reflect(dynamic). So these aren`t helping if I only have a String.
In Java you can do this pretty easily, by calling Class.forName(String). Then you would get a Constructor instance, make it accessibly and call it.
Does anyone know if this is even possible in dart? What seems weird is that once you have a ClassMirror you can access fields and methods by passing symbols, which can be created by Strings.
You can put a specific list of strings to map to a specific list of closures to create a new object with specific parameters.
But you can't get a reflection without using dart:mirrors, which is being deprecated, and also had a negative impact on tree shaking to get the payload size down.
In general, you're invited to look at the package:reflectable to achieve most of what you'd want out of dart:mirrors, using source-to-source builders.
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 something like this:
class MyClass
{
static void DoSomething(arg1, arg2){...}
}
Via reflection, I am able to get the ClassMirror of this class. From this point, how would I get to the concrete static function so I can call it.
Note that I tried to use:
ObjectMirror.invoke('DoSomething', [arg1, arg2]);
which would initially appear to work, but it doesn't support passing of complex types as arguments, This static function requires a complex type as one of it's arguments.
Ideally, I'd like to get the 'Function' object that represents the static method so I can invoke it directly.
a. The current state of affairs is temporary. The plan is that the mirror API will wrap the arguments with mirrors for you.
b. The API may eventually support a getProperty method that will give you a Future on the function object. However, you will not get a Function object directly, so this won't really make any difference in this case.
c. The core idea is that the API fundamentally works on mirrors. To make it more usable, it should accept non-mirrors as input and wrap them in mirrors for you. It will always return mirrors, and in some cases return futures on these. This is so the API works the same for remote and local cases.
d. Resources for understanding mirrors:
http://www.bracha.org/mirrors.pdf (academic paper, tough going)
http://www.hpi.uni-potsdam.de/hirschfeld/events/past/media/100105_Bracha_2010_LinguisticReflectionViaMirrors_HPI.mp4 (a video, pre-Dart, discusses earlier Mirror systems)
http://gbracha.blogspot.com/2010/03/through-looking-glass-darkly.html (an old, pre-dart, blog post of mine on mirrors)
http://www.wirfs-brock.com/allen/posts/228 (Allen Wirfs-Brock's blog. Allen was a mirror pioneer back in Smalltalk in the 90s)
http://www.wirfs-brock.com/allen/posts/245
You can also search my blog, or Allen Wirf-Brock's for posts on the topic.