I have a c code like this
int x;
x = 5;
I used eclipse cdt to generate the AST, and traverse on it, so this is the code of the traversed class
public class RuleChk extends AbstractRule {
public RuleChk(IASTTranslationUnit ast) {
super("RuleChk", false, ast);
shouldVisitDeclarations = true;
shouldVisitParameterDeclarations = true;
}
#Override
public int visit(IASTSimpleDeclaration simpleDecl) {
//if this node has init, e.g: x = 5, do business
if(VisitorUtil.containNode(simpleDecl, CASTExpressionStatement){
// Now I have the x = 5 node,
// I want to get the reference node of it's declaration
// I mean (int x;) node
IASTNode declNode = ?????
}
return super.visit(parameterDeclaration);
}
}
what I want to visit the node that only has assignation(Initialization) and get the reference of declaration node for that varaiable.
I'm not sure how VisitorUtil works (it's not from the CDT code), but I assume it gives you a way to access the the found node. So:
Given the IASTExpressionStatement node that was found, use IASTExpression.getExpression() to get the contained expression.
See if it's an IASTBinaryExpression, and that is getOperator() is IASTBinaryExpression.op_assign.
Use IASTBinaryExpression.getOperand1() to get the assignment expression's left subexpression. Check that it's an IASTIdExpression, and get the variable it names via IASTIdExpression.getName().
Now that you have the name, use IASTName.resolveBinding() to get the variable's binding. This is the variable's representation in the semantic program model.
To find the variable's definition, use IASTTranslationUnit.getDefinitionsInAST(IBinding) if you only want it to look in the current file, or IASTTranslationUnit.getDefinitions(IBinding) if you want it to look in included header files as well (the latter requires the project to be indexed). The IASTTranslationUnit can be obtained from any IASTNode via IASTNode.getTranslationUnit().
Related
Is there a construct that communicates to the type checker a function's post-condition?
For example, in typescript it is possible to say
function assertIsNumber(value: any): asserts value is number {
if (typeof value !== 'number') {
throw new TypeError();
}
}
I would like to be able to do something like the following in dart:
class SomeClass {
int? value;
_checkPreconditions() {
if(value == null) {
throw MyPreconditionError()
}
// ...
}
somefunc() {
_checkPreconditions();
// here we know `value` is a non-null int.
final sum = value + 5;
}
}
I understand I could coerce the value to non-null sum = value! + 5, but I would prefer to allow the function to inform the type checker if possible.
It looks like the type system of Dart is not so powerful. The only thing that looks (from first glance) possible is to create a custom code analyzer package (or search for one that already exists).
Dart annotations don't actually do anything. They provide hints to tools such as the Dart analyzer (usually so that it can generate additional warnings), but they cannot change program behavior. Even if you could convince the analyzer to treat some variables as different types, you still wouldn't be able to compile and run your code.
Annotations can be used by code generation tools, so one possibility might be to generate a statement such as final value = this.value!; automatically. However, that would be a lot of trouble to go through (and would mean that code then would need to use this.value = 42; for assignments and would prevent your code from being analyzed directly).
class X extends Y {
X(int a, int b) : super(a,b);
}
Can someone give me an explanation about the syntax meaning of the colon :?
This feature in Dart is called "initializer list".
It allows you to initialize fields of your class, make assertions and call the super constructor.
This means that it is not the same as the constructor body. As I said, you can only initialize variables and only access static members. You cannot call any (non-static) methods.
The benefit is that you can also initialize final variables, which you cannot do in the constructor body. You also have access to all parameters that are passed to the constructor, which you do not have when initializing the parameters directly in the parentheses.
Additionally, you can use class fields on the left-hand of an assignment with the same name as a parameter on the right-hand side that refers to a parameter. Dart will automatically use the class field on the left-hand side.
Here is an example:
class X {
final int number;
X(number) : number = number ?? 0;
}
The code above assigns the parameter named number to the final field this.number if it is non-null and otherwise it assigns 0. This means that the left-hand number of the assignment actually refers to this.number. Now, you can even make an assertion that will never fail (and is redundant because of that, but I want to explain how everything works together):
class X {
final int number;
X(number): number = number ?? 0, assert(number != null);
}
Learn more.
It's ok to access non static member in initializer list.
class Point {
num x, y;
Point(this.x, this.y);
Point.origin(): this.x = 10, this.y = 10;
}
main() {
Point p = Point.origin();
print(p.x); // 10
}
I'm guessing this question is going to apply to many similar languages other than MQL4 such as c++ (which I also forget how to use) which require you manually specify when you are passing by reference.
Method reference:
int[] previous = GetPrevious(i, ZigZagBuffer);
Method definition:
int GetPrevious[](int current, const double& buffer[])
{
int count = 0;
int result[];
// calculate count
ArrayResize(result,count);
// fill array
return result;
}
The resulting compile error is:
"Invalid Array Access"
From what I understand, this is because array's can only be passed by reference, but you have to explicitly state that you are passing it by reference. But the more I look up the syntax for passing by reference, the more I find articles about passing parameter by reference. (which I already know how to do as you can see in the code example.)
What is the syntax to assign the output of a method to a variable?
In case it matters, I only need to read the array multiple times; I'm not needing to alter or re-assign it after it is declared.
You cannot return array. You have to create it and pass into the function, fill inside the function and that's it.
OnTick(){
double array[]; //declaration of the array
fillArray(array,10); //passing array by ref, updating it there
Print(array[0]=0 && array[9]=9);//returns true
}
void fillArray(double &array[],int size){
ArrayResize(array,size);
for(int i=0;i<size;i++){array[i]=i;}
}
I am looking for examples of Chapel passing by reference. This example works but it seems like bad form since I am "returning" the input. Does this waste memory? Is there an explicit way to operate on a class?
class PowerPuffGirl {
var secretIngredients: [1..0] string;
}
var bubbles = new PowerPuffGirl();
bubbles.secretIngredients.push_back("sugar");
bubbles.secretIngredients.push_back("spice");
bubbles.secretIngredients.push_back("everything nice");
writeln(bubbles.secretIngredients);
proc kickAss(b: PowerPuffGirl) {
b.secretIngredients.push_back("Chemical X");
return b;
}
bubbles = kickAss(bubbles);
writeln(bubbles.secretIngredients);
And it produces the output
sugar spice everything nice
sugar spice everything nice Chemical X
What is the most efficient way to use a function to modify Bubbles?
Whether Chapel passes an argument by reference or not can be controlled by the argument intent. For example, integers normally pass by value but we can pass one by reference:
proc increment(ref x:int) { // 'ref' here is an argument intent
x += 1;
}
var x:int = 5;
increment(x);
writeln(x); // outputs 6
The way that a type passes when you don't specify an argument is known as the default intent. Chapel passes records, domains, and arrays by reference by default; but of these only arrays are modifiable inside the function. ( Records and domains pass by const ref - meaning they are passed by reference but that the function they are passed to cannot modify them. Arrays pass by ref or const ref depending upon what the function does with them - see array default intent ).
Now, to your question specifically, class instances pass by "value" by default, but Chapel considers the "value" of a class instance to be a pointer. That means that instead of allowing a field (say) to be mutated, passing a class instance by ref just means that it could be replaced with a different class instance. There isn't currently a way to say that a class instance's fields should not be modifiable in the function (other than making them to be explicitly immutable data types).
Given all of that, I don't see any inefficiencies with the code sample you provided in the question. In particular, here:
proc kickAss(b: PowerPuffGirl) {
b.secretIngredients.push_back("Chemical X");
return b;
}
the argument accepting b will receive a copy of the pointer to the instance and the return b will return a copy of that pointer. The contents of the instance (in particular the secretIngredients array) will remain stored where it was and won't be copied in the process.
One more thing:
This example works but it seems like bad form since I am "returning" the input.
As I said, this isn't really a problem for class instances or integers. What about an array?
proc identity(A) {
return A;
}
var A:[1..100] int;
writeln(identity(A));
In this example, the return A in identity() actually does cause a copy of the array to be made. That copy wasn't created when passing the array in to identity(), since the array was passed by with a const ref intent. But, since the function returns something "by value" that was a reference, it's necessary to copy it as part of returning. See also arrays return by value by default in the language evolution document.
In any case, if one wants to return an array by reference, it's possible to do so with the ref or const ref return intent, e.g.:
proc refIdentity(ref arg) ref {
return arg;
}
var B:[1..10] int;
writeln(refIdentity(B));
Now there is no copy of the array and everything is just referring to the same B.
Note though that it's currently possible to write programs that return a reference to a variable that no longer exists. The compiler includes some checking in that area but it's not complete. Hopefully improvements in that area are coming soon.
I am currently using ReSharper V8.1. I've only recently began using ReSharper and have found some interest in their LiveTemplate Macros. I've conjured up a solution to return a list of HotspotItems from a constant, similar to ReSharper's predefined macro "Comma-delimited list of values". In the method I take the constant variable of the template parameter and do a split string on them to provide a collection of HotSpotItems. Unfortunately it doesn't work if I use the macro more than one time within a template. Below is an extreme hack job showing my implementation of the method HotspotItems of IMacroImplementation.
I am hoping that someone out there may have done some work in this area and could possibly provide an example of how they've implemented IMacroImplementation which provides a list of items from a constant and also allows for multiple uses within a single template.
Thank you.
public override HotspotItems GetLookupItems(IHotspotContext context)
{
HotspotItems hotSpotItems = null;
foreach (var hotspot in context.HotspotSession.Hotspots)
{
if (hotspot.Expression != null && ((MacroCallExpressionNew)hotspot.Expression).Definition is Macros.DisplayMultipleItems)
{
//hotspot.CurrentValue
var multiItems = ((MacroCallExpressionNew) hotspot.Expression).Definition as DisplayMultipleItems;
if (!multiItems.ItemSet)
{
var expression = hotspot.Expression as MacroCallExpressionNew;
IMacroParameterValueNew baseValue = expression.Parameters[0].GetValue(context.SessionContext.Solution.GetLifetime(), context.HotspotSession);
string templateValue = baseValue.GetValue();
multiItems.ItemSet = true;
if (!string.IsNullOrEmpty(templateValue) && templateValue.Split(',').Any())
{
var lookupItems = templateValue.Split(',').Select(param => new TextLookupItem(param)).Cast<ILookupItem>().ToList();
if (hotSpotItems == null)
hotSpotItems = new HotspotItems(lookupItems);
else
{
foreach (var item in lookupItems)
{
hotSpotItems.Items.Add(item);
}
}
}
}
}
}
return hotSpotItems;
}
You should fire up dotPeek and point it to the ReSharper bin directory and take a look at ListMacroDef and ListMacroImpl, which is the implementation for the comma-delimited list macro.
The definition derives from SimpleMacroDefinition. It gets given the parameters in the call to GetPlaceholder, looks at the first and splits it by comma, returning the first item as the placeholder.
ListMacroImpl is just as simple. Its constructor has an [Optional] parameter of type MacroParameterValueCollection. This is the list of parameter values specified in the hotspot editor. You'll want to check for null and take the first parameter, which will be your delimited list. It then overrides GetLookupItems and returns HotspotItems.Empty if the parameter value is null, or parses the value and returns a list of TextLookupItem.
You don't need to look at the session and list of hotspots - that will get you all hotspots in the session, when you're only interested in the current hotspot, and ReSharper will create a new IMacroImplementation for each hotspot and give you those values in your constructor.