I'm trying to break down a library into parts, and having trouble accessing private elements of the library from a part.
For example, say I have a file named stack.dart with the following content:
library stack;
final _stack = [];
get isEmpty => _stack.isEmpty;
get top => isEmpty ? throw "Empty stack!" : _stack.last;
get pop => isEmpty ? throw 'Empty stack!' : _stack.removeLast();
push(elt){
_stack.add(elt);
return elt;
}
I also have another file with the following contents:
part of stack;
display(){
print(_stack); // can't access _stack from here!
}
Is this to be expected or am I doing something wrong?
Is _stack private to the library or the file?
Your problem is you have forgotten to include you file into the library by using the part keyword:
lib.dart:
library test_lib;
part 'part.dart';
final _private = 'This is private';
part.dart:
part of test_lib;
void test() {
print(_private); // I have access to the _private variable defined in lib.dart
}
Related
I have stored variables in a class with their code names.
Suppose I want to get XVG from that class, I want to do
String getIconsURL(String symbol) {
var list = new URLsList();
//symbol = 'XVG'
return list.(symbol);
}
class URLsList{
var XVG = 'some url';
var BTC = 'some url';
}
Can someone help me achieve this or provide me with a better solution?
Dart when used in flutter doesn't support reflection.
If it's text that you want to have directly in your code for some reason, I'd advise using a text replace (using your favourite tool or using intellij's find + replace with regex) to change it into a map, i.e.
final Map<String, String> whee = {
'XVG': 'url 1',
'BTC': 'url 2',
};
Another alternative is saving it as a JSON file in your assets, and then loading it and reading it when the app opens, or even downloading it from a server on first run / when needed (in case the URLs need updating more often than you plan on updating the app). Hardcoding a bunch of data like that isn't necessarily always a good idea.
EDIT: how to use.
final Map<String, String> whee = .....
String getIconsURL(String symbol) {
//symbol = 'XVG'
return whee[symbol];
}
If you define it in a class make sure you set it to static as well so it doesn't make another each time the class is instantiated.
Also, if you want to iterate through them you have the option of using entries, keys, or values - see the Map Class documentation
I'd just implement a getProperty(String name) method or the [] operator like:
class URLsList{
var XVG = 'some url';
var BTC = 'some url';
String get operator [](String key) {
switch(key) {
case 'XVG': return XVG;
case 'BTC': return BTC;
}
}
}
String getIconsURL(String symbol) {
var list = new URLsList();
return list[symbol];
}
You can also use reflectable package that enables you to use reflection-like code by code generation.
Assuming that the class is being created from a JSON Object, you can always use objectName.toJSON() and then use the variable names are array indices to do your computations.
According to the readme for the Dart-Yaml pub package, I should be able to do the following:
var db = loadYamlDocument("db.yaml");
with print(db['hostname']); giving me the value I have specified for port in that yaml, however I'm told that YamlDocument has no instance method []. Okay, I guess that object doesn't have map behaviors, which is something I would have expected it to have. Looking through the docs, there's mention of a YamlMap, but I don't see how to implement that at all.
If I simply try print(db); I actually get the string: 'db.yaml'.
So I tried using new File('db.yaml'); and then sending that variable into the loadYamlDocument method, but that doesn't work either.
Does anyone have any luck reading a yaml document and getting a map out of it in Dart?
import "dart:io";
import "package:yaml/yaml.dart";
main() {
File file = new File('pubspec.yaml');
String yamlString = file.readAsStringSync();
Map yaml = loadYaml(yamlString);
}
EDIT:
Map loadYamlFileSync(String path) {
File file = new File(path);
if (file?.existsSync() == true) {
return loadYaml(file.readAsStringSync());
}
return null;
}
Future<Map> loadYamlFile(String path) async{
File file = new File(path);
if ((await file?.exists()) == true) {
String content = await file.readAsString();
return loadYaml(content);
}
return null;
}
main(List<String> args){
print(loadYamlFileSync("pubspec.yaml"));
}
Check the documentation pages for the Yaml package.
loadYamlDocument() returns a YamlDocument which is a 'heavyweight' class that gives you access to all the features of a Yaml document.
You probably want to use loadYaml, which in most cases is going to return a Map. The description says that the actual implementation of the map is a YamlMap (the Yaml package's implementation of a Map, that they presumably need to use instead of a HashMap for some technical reason).
I would like to use clang to preprocess objective C files from an iOS app. I looked over the source code and am trying to implement a pre-processor based on the RecursiveASTVisitor class. However, I seem to be running into many issues that I cannot resolve. I developed a preprocessor to add a "Enter" call at the beginning of each method and an "Exit" call at the end. I also added an "Exit" call before each return statement. I am using the following code to do the instrumentation:
class ExampleVisitor : public RecursiveASTVisitor<ExampleVisitor> {
private:
ASTContext *astContext; // used for getting additional AST info
std::string funcName;
public:
explicit ExampleVisitor(CompilerInstance *CI)
: astContext(&(CI->getASTContext())) // initialize private members
{
rewriter.setSourceMgr(astContext->getSourceManager(), astContext->getLangOpts());
}
virtual bool VisitObjCMethodDecl(ObjCMethodDecl *ND) {
funcName = ND->getDeclName().getAsString();
errs() << "Testing function: " << funcName << "\n";
if (ND->hasBody()) {
rewriter.InsertText(ND->getBody()->getSourceRange().getBegin().getLocWithOffset(1), "\nEnter(\""+funcName+"\");\n");
rewriter.InsertText(ND->getBody()->getSourceRange().getEnd(),"Exit(\""+funcName+"\");\n");
}
return true;
}
virtual bool VisitReturnStmt(ReturnStmt *ret) {
rewriter.InsertText(ret->getSourceRange().getBegin(), "\nExit(\""+funcName+"\");\n");
errs() << "** Rewrote ReturnStmt\n";
return true;
}
virtual ~ExampleVisitor() {}
};
class ExampleASTConsumer : public ASTConsumer {
private:
ExampleVisitor *visitor; // doesn't have to be private
public:
// override the constructor in order to pass CI
explicit ExampleASTConsumer(CompilerInstance *CI)
: visitor(new ExampleVisitor(CI)) // initialize the visitor
{ }
// override this to call our ExampleVisitor on the entire source file
virtual void HandleTranslationUnit(ASTContext &Context) {
/* we can use ASTContext to get the TranslationUnitDecl, which is
a single Decl that collectively represents the entire source file */
visitor->TraverseDecl(Context.getTranslationUnitDecl());
}
};
The code compiles. I created a command line executable "instrument". I then used the following command to run this on a simple Objective C program generated by Xcode:
instrument AppDelegate.m --
I run into two problems. First, I get the error: 'UIKit/UIKit.h' file not found. This is one of the includes generated by Xcode. Second, I'm seeing only some of the return statements being processed in the file. Can someone give me some insights into what is happening?
I'm using the 3.7.0 version of llvm.
In Dart, is it possible for a function to have a prototype associated with it?
Example Javascript code:
doStuff.prototype.isDefined = true; //is there anything like Javascript's function prototypes in Dart?
function doStuff(){
console.log("The function doStuff was called!");
}
Is it possible to do the equivalent of this in Dart (i.e., create a list of properties for each function?)
Two things to address here:
First, Dart doesn't have prototypes or prototypal inheritance, and instead uses classical inheritance. Rather than a prototype, objects have a class, and instead of a prototype chain, objects have superclasses.
Second, for your specific case, I think we'd have to see more of what you need to do to figure out the idiomatic way to do it in Dart. It should soon be possible to emulate functions with objects so that you can invoke an object and still have state and other methods associated with it.
See this article for more: http://www.dartlang.org/articles/emulating-functions/
When that capability lands you'll be able to do this:
class DoStuff {
bool isDefined = true;
call() => print("The function doStuff was called!");
}
var doStuff = new DoStuff();
main() => doStuff();
Which works if you have a fixed set of metadata about your function that you need to keep track of. It's slightly different from JavaScript because each instance of the function in Dart will have its own state for isDefined. I'm not sure if it's possible or easy to get multiple instances of the function in JavasScript, but you might need to make isDefined static so that the value is shared across all instances.
Dart does not allow you to add or remove member variables from an instance of a class at runtime. Rewriting your example in Dart it might look something like this:
class doStuff {
bool isDefined;
doStuff() {
isDefined = true;
}
void stuff() {
print('The function stuff was called!');
}
}
main() {
new doStuff().stuff();
}
If you wanted to add a property bag to a class in Dart you would write:
class PropertyObject {
Map<String, Dynamic> properties;
PropertyObject() {
properties = new Map<String, Dynamic>();
}
Dynamic operator[](String K) => properties[K];
void operator[]=(String K, Dynamic V) => properties[K] = V;
}
main() {
PropertyObject bag = new PropertyObject();
bag['foo'] = 'world';
print('Hello ${bag['foo']}');
}
Note that you can't access map properties using the '.' operator.
I am writing a library in Dart and I have static files under the library folder. I want to be able to read those files, but I'm not sure how to retrieve the path to it... there is not __FILE__ or $0 like in some other languages.
Update: It seems that I was not clear enough. Let this help you understand me:
test.dart
import 'foo.dart';
void main() {
print(Foo.getMyPath());
}
foo.dart
library asd;
class Foo {
static Path getMyPath() => new Path('resources/');
}
It gives me the wrong folder location. It gives me the path to test.dart + resources/, but I want the path to foo.dart + resources/.
As mentioned, you can use mirrors. Here's an example using what you wanted to achieve:
test.dart
import 'foo.dart';
void main() {
print(Foo.getMyPath());
}
foo.dart
library asd;
import 'dart:mirrors';
class Foo {
static Path getMyPath() => new Path('${currentMirrorSystem().libraries['asd'].url}/resources/');
}
It should output something like:
/Users/Kai/test/lib/resources/
There will probably be a better way to do this in a future release. I will update the answer when this is the case.
Update: You could also define a private method in the library:
/**
* Returns the path to the root of this library.
*/
_getRootPath() {
var pathString = new Path(currentMirrorSystem().libraries['LIBNAME'].url).directoryPath.toString().replaceFirst('file:///', '');
return pathString;
}
The dart mirrors API (still experimental, and not available on all platforms such as dart2js yet) exposes a url getter on the LibraryMirror. This should give you what you want.
I'm not aware of any other way to get this information on a library.
#import('dart:mirrors');
#import('package:mylib/mylib.dart');
main(){
final urlOfLib = currentMirrorSystem().libraries['myLibraryName'].url;
}
Generally the usual method of accessing resources which are located at a static position with your library is by use using a relative path.
#import('dart:io');
...
var filePath = new Path('resources/cool.txt');
var file = new File.fromPath(filePath);
// And if you really wanted, you can then get the full path
// Note: below is for example only. It is missing various
// integrity checks like error handling.
file.fullPath.then((path_str) {
print(path_str);
});
See addition API information on Path and on File
As an aside.. If you absolutely wanted to get the same type of output as __FILE__ you can do something like the following:
#import('dart:io');
...
var opts = new Options();
var path = new Path(opts.script);
var file = new File.fromPath(path);
file.fullPath().then((path_str) {
print(path_str);
});