I'm trying to create a simple class with a member function that would print out some member values, but I'm getting errors when I try to reference 'self':
attempt to index global 'self' (a nil value)
Here's the script I'm trying to run:
Test = {}
function Test:new()
T = {}
setmetatable(T, self)
self.__index = self
self.Name = "Test Object"
return T
end
function Test:printName()
print("My name is " .. self.Name) -- This causes the error
end
I've also tried self:Name but I get a similar error. What am I doing wrong here?
EDIT:
Forgot to mention that I call the printName() function from C++ code. If I call the function from Lua, it works properly.
The Test object is created in Lua and a callback function is done. The callback is called in C++ like this:
luabridge::LuaRef testObjectRef = ...; // This is populated from Lua, refers to the printName() function
testObjectRef(); // Calls the function
The callback in the script is done like this:
-- in Test:new()
self.Callback = LuaCallback(self.printName)
Helper.setCallback(self.Callback)
The callback itself works fine if I don't try to refer to self. The error comes up only when I try to do that.
I took your code, added:
local test = Test:new()
test:printName()
It gives me the correct output.
My name is Test Object
If you're calling it via C API, you have to remember to manually push the self argument onto the stack. Remember that:
obj:fun() ~ obj.fun(obj)
I managed to fix the problem. I added the self as an extra argument in the listener constructor and passed it as the first parameter to the callback function.
-- in the script
self.Callback = LuaCallback(self, self.printName)
Helper.setCallback(self.Callback)
Related
I am using Java code and converting the code in ColdFusion. There are some challenges where I am stuck. This is one function I have in Java:
import com.jayway.jsonpath.JsonPath;
import net.minidev.json.JSONArray;
import net.minidev.json.JSONStyle;
private static String getDetails(String instaDetailsElement) {
String jsonResponse = instaDetailsElement.split(" = ")[1];
JSONArray mediaArray = JsonPath.read(jsonResponse, "$.entry_data.PostPage[:1].graphql.shortcode_media");
String returnJsonString = mediaArray.toJSONString(new JSONStyle(JSONStyle.FLAG_IGNORE_NULL));
System.out.println(returnJsonString);
return returnJsonString;
}
These two lines are giving me some trouble:
var mediaArray = JsonPath.read(jsonResponse, "$.entry_data.PostPage[:1].graphql.shortcode_media");
var returnJsonString = mediaArray.toJSONString(new JSONStyle(JSONStyle.FLAG_IGNORE_NULL));
Here is what I attempted so far. I loaded the jar library for JSON path and tried using it like this:
Application.cfc settings
<cfset this.javaSettings = {LoadPaths = ["cfc/jar"], loadColdFusionClassPath = true, reloadOnChange = false}>
CF Code:
public any function getDetails(String instaDetailsElement) {
var jsonResponse = instaDetailsElement.split(" = ")[1];
var JsonPath = Createobject("java","com.jayway.jsonpath.JsonPath");
writedump(application);
var mediaArray = JsonPath.read(jsonResponse, "$.entry_data.PostPage[:1].graphql.shortcode_media");
writedump(mediaArray); abort;
var returnJsonString = mediaArray.toJSONString(new JSONStyle(JSONStyle.FLAG_IGNORE_NULL));
return returnJsonString;
}
I'm able to view the class methods when I dump the JsonPath object (screen shot), but when I try to call JsonPath.read() I get this error:
No matching Method for read(string, string) found for
com.jayway.jsonpath.JsonPath
TL;DR;
No matching method for read(string, string) found for com.jayway.jsonpath.JsonPath
Technically the error message is correct: there is no read() method that accepts two strings (even though that's how it's used in the java code). The method actually expects three arguments:
Pass in an empty array for the 3rd argument:
JsonPath.read(jsonResponse, "$.entry_data.PostPage[:1].graphql.shortcode_media", []);
Explanation:
String jsonResponse = instaDetailsElement.split(" = ")[1];
JsonPath.read(jsonResponse, "$.entry_data.PostPage[:1].graphql.shortcode_media")
If there really is no read(String, String) method, you might wonder why the java code works at all, since that's exactly what it uses. It works due to a special feature of java.
The documentation shows the overloaded read(..) method actually has three parameters, but one of them is special:
read(String json,
String jsonPath,
Predicate... filters)
Notice the ... after the class name (Predicate)? It's a construct called "varargs" (or variable number of arguments):
You can use a construct called varargs to pass an arbitrary number of values to a method. You use varargs when you don't know how many of a
particular type of argument will be passed to the method. It's a
shortcut to creating an array manually ...
To use varargs, you follow the type of the last parameter by an ellipsis (three dots, ...), then a space, and the parameter name. The
method can then be called with any number of that parameter,
including none.
So in java you're allowed to omit the third argument entirely and call read(String, String) with two strings. ColdFusion doesn't support that syntax, because it creates too much ambiguity. So in lieu of omitting the argument, you can pass in an empty array instead:
JsonPath.read(jsonResponse, "$.entry_data.PostPage[:1].graphql.shortcode_media", []);
(Since this has turned into two questions in one thread, I'm separating the second answer out for clarity ...)
var returnJsonString = mediaArray.toJSONString(new JSONStyle(JSONStyle.FLAG_IGNORE_NULL));
As for translating the JSONStyle code, it helps to unpack nested code from the inside out. Then tackle each piece separately:
mediaArray.toJSONString(new JSONStyle( JSONStyle.FLAG_IGNORE_NULL ));
mediaArray.toJSONString( new JSONStyle( JSONStyle.FLAG_IGNORE_NULL ) )
mediaArray.toJSONString( new JSONStyle( JSONStyle.FLAG_IGNORE_NULL ) )
Piece #1
Uses a static field of the JSONStyle class named FLAG_IGNORE_NULL. To access the field, create a reference to that class:
JsonStyle = createObject("java", "net.minidev.json.JSONStyle");
writeDump(JSONStyle.FLAG_IGNORE_NULL);
Piece #2
Creates a brand new instance of the JSONStyle class, using the static field from above. Use createObject() to create the new instance, passing the static field into the psuedo constructor init():
newJsonStyle = createObject("java", "net.minidev.json.JSONStyle").init(JSONStyle.FLAG_IGNORE_NULL);
writeDump( newJsonStyle );
Piece #3
All that's left is calling the JSONArray.toJSONString() method with the JSONStyle object you just created:
result = mediaArray.toJSONString( newJsonStyle );
writeDump(result);
In the context of a Flutter 2.0.5 app whose state I'd like to manage with Riverpod, I thought I can declare a StateNotifierProvider like this:
import 'package:flutter_riverpod/flutter_riverpod.dart';
final counterProvider = StateNotifierProvider<CounterStateNotifier>((ref) => CounterStateNotifier());
class CounterStateNotifier extends StateNotifier<int> {
CounterStateNotifier([int count = 0]) : super(count);
void increment() => state++;
}
But Android Studio (and later the Dart compiler as well) complains about the line where I declare the counterProvider variable:
The type 'StateNotifierProvider' is declared with 2 type parameters, but 1 type arguments were given.
Removing the <CounterStateNotifier> type parameter in StateNotifierProvider<CounterStateNotifier> removes the error. However, attempting to read the provider and call its increment method (setting () => context.read(counterProvider).increment() as the onPressed of an ElevatedButton, then pressing the button) gives the following runtime error:
'increment'
method not found
Receiver: 0
Arguments: []
Why is context.read(counterProvider) returning the int state instead of the notifier? And what is the reason behind the type parameter error mentioned in the first part of my question?
I should mention that I'm running my app on the web (with flutter run -d Chrome).
As of Riverpod 0.14.0, State is the default value exposed by StateNotifierProvider.
The syntax for declaring your StateNotifierProvider is now as follows:
final counterProvider = StateNotifierProvider<CounterStateNotifier, int>((ref) => CounterStateNotifier());
Accessing functions now requires adding .notifier (accessing the StateNotifier itself):
context.read(counterProvider.notifier).increment();
And like you've noticed, you now access the state like so:
final count = context.read(counterProvider);
More on the changes here.
You may also use dynamic to accept any type if value for the StateNotifierProvider
final modelProvider =
StateNotifierProvider.autoDispose<ModelClassName, dynamic>(
(ref) => ModelClassName());
I am working on JNI program and I am not able to call a java method from my C++ program.
The code snippet of java method is here
public static void getTables(Connection conn) throws Exception {
String TABLE_NAME = "TABLE_NAME";
String TABLE_SCHEMA = "TABLE_SCHEM";
String[] TABLE_TYPES = {"TABLE"};
DatabaseMetaData dbmd = conn.getMetaData();
ResultSet tables = dbmd.getTables(null, null, null, TABLE_TYPES);
while (tables.next()) {
System.out.println(tables.getString(TABLE_NAME));
System.out.println(tables.getString(TABLE_SCHEMA));
}
}
And I want to call this java method from C++ program.
I am able to call the main method
for that the code is
midMain = env->GetStaticMethodID(clsH, "main", "([Ljava/lang/String;)V");
I want to call getTables method like this. Please help me to solve it.
Please see
https://stackoverflow.com/a/14872927/755804
and probably these:
https://stackoverflow.com/a/14021142/755804
https://stackoverflow.com/a/15941319/755804
https://stackoverflow.com/a/21109940/755804
There is some difference between calling static and non-static methods, but not much.
I suggest you start with something that works and gradually change it to what you want.
I am using a proxy/delegate pattern in a coldfusion component, and am getting unexpected results (from my point of view). Below is my proxy component - its pretty straight forward, I just init the CFC with the actual component I want to delegate to, and then map the named functions from that CFC through to a proxy function (the below is simplified for this example)
I have created a proxy component as follows:
component output="false"{
/** Constructor for proxy - requires an instance of myFusebox **/
public MyFuseboxProxy function init( Required any myFb ){
variables.myFusebox = arguments.myFb;
return this;
}
this.do = variables.proxy;
this.getApplication = variables.proxy;
this.getApplicationData = variables.proxy;
private any function proxy(){
var local.functionName = getFunctionCalledName();
var local.function = variables.myFusebox[local.functionName];
var local.returnVal = local.function( argumentCollection=arguments );
return local.returnVal;
}
}
From my application I call the following code:
variables.myFusebox = new ab.MyFuseboxProxy( variables.myFusebox );
variables.myFusebox.getApplicationData().startTime = now();
Now, in the above scenario, I would expect my proxy component to map the getApplicationData() function straight through to the original myFusebox component (via my proxy() function).
That function in the underlying component is as follows:
<cffunction name="getApplicationData" returntype="struct" access="public" output="false"
hint="I am a convenience method to return a reference to the application data cache.">
<cfreturn getApplication().getApplicationData() />
</cffunction>
That proxy all works fine, however, once I am in the above function in the original myFusebox I get the following error:
Message: Variable GETAPPLICATION is undefined.
StackTrace: coldfusion.runtime.UndefinedVariableException: Variable GETAPPLICATION is undefined.
And if I dump "this" inside that function, it actually dumps my proxy object.
Can anyone explain this or what I have done wrong? I was expecting that once the function call was inside the underlying object, it would just use its own context from there (my proxy just being a pass through really to the delegate)
I think this is the key point:
I was expecting that once the function call was inside the underlying
object
You've got this:
private any function proxy(){
var local.functionName = getFunctionCalledName();
var local.function = variables.myFusebox[local.functionName];
var local.returnVal = local.function( argumentCollection=arguments );
return local.returnVal;
}
When you do this bit:
var local.function = variables.myFusebox[local.functionName];
you are effectively pulling the function referenced by local.functionName out of variables.myFusebox, and putting it into the current function, within the context of your MyFuseboxProxy instance.
So when you do this:
var local.returnVal = local.function( argumentCollection=arguments );
You are not running variables.myFusebox[local.functionName]() (so in the context of variables.myFusebox), but you are running local.function() (so in the context of your proxy object).
I don't have the patience to try to follow your logic here, but I am still surprised you get that error. I would have expected this to happen:
local.function (a reference to getApplicationData from variables.myFusebox) runs getApplication().
getApplication() in the context of the MyFuseboxProxy instance should be a reference to variables.proxy().
variables.proxy() resolves the proxied function as getApplication(), and pulls that out of variables.myFusebox, and runs it in the context of your MyFuseboxProxy instance.
You do not include the code of the getApplication() function from variables.myFusebox, so I dunno what would happen next, but this is not what you want to be happening.
Anyway, the crux is - I think - that instead of running the functions inside variables.myFusebox, you're running them in your MyFuseboxProxy instance instead. If you want to do this sort of proxying (and ignoring for a moment you have invoke() specifically for doing this), you need to still call the function in its original context, not reference it in some new context.
I guess you're doing all this horsing around because ColdFusion doesn't like this syntax:
someObject[someMethodName]()
It baulks at the []() notation. However the solution is not this:
someOutOfContextReference = someObject[someMethodName]
result = someOutOfContextReference()
It's this:
someObject.someInContextReference = someObject[someMethodName]
result = someObject.someInContextReference()
See the subtle difference?
ColdFusion functions are not intrinsically closures, which is what you'd need them to be to work the way you want.
I am trying to work out the correct <cfscript> syntax for calling a dynamic method within ColdFusion 9. I have tried a number of variations and had a good search around.
<cfinvoke> is clearly the tag I want, sadly however I cannot use this within my pure cfscript component as it was implemented in ColdFusion 10.
i.e coldfusion 9 dynamically call method
I have tried the following within my CFC:
/** Validate the method name **/
var resources = getResources();
if (structKeyExists(variables.resources, name)) {
variables.resourceActive[name] = true;
var reflectionMethod = resources[name];
var result = "#reflectionMethod.getMethodName()#"(argumentCollection = params);
}
Where the return value of reflectionMethod.getMethodName() is the method name I want to call. It is 100% returning the correct value (the name of the method) where that method is correctly defined and accessible,
My error is a syntax error on that line.
You don't want to get the method name, you want to get the actual method, eg something like:
function getMethod(string method){
return variables[method];
}
The call that, thus:
theMethod = getMethod(variableHoldingMethodName);
result = theMethod();
Unfortunately one cannot simply do this:
result = getMethod(variableFoldingMethodName)();
Or:
result = myObject[variableFoldingMethodName]();
As the CF parser doesn't like the double-up of the parentheses or brackets.
The caveat with the method I suggested is that it pulls the method out of the CFC, so it will be running in the context of the calling code, not the CFC instance. Depending on the code in the method, this might or might not matter.
Another alternative is to inject a statically-named method INTO the object, eg:
dynamicName = "foo"; // for example
myObject.staticName = myObject[dynamicName];
result = myObject.staticName(); // is actually calling foo();
Assuming the method is in your current (variables) scope, you could try:
var result = variables[reflectionMethod.getMethodName()](argumentCollection = params);