var persons: List<Person> = readPersonsFile("persons.txt");
ListSort.sort(persons, function(personA, personB): Int
{
return Person.compare(personA.first(), personB.first());
});
I'm just trying to sort this list. It's giving me this error:
Constraint check failure for sort.T
List<Person> should be { prev : List<Person>, next : List<Person> }
List<Person> has no field next
Which is wierd to me, because it sounds like it's wanting me to pass an implicit object with two different lists, which if that's really the way... that's not very insulated if that's true.
ListSort is only supposed to work on singly or doubly linked lists; the List class is neither of these (although it does share some APIs with them, but with different time and space costs).
In your case, you can probably change readPersonsFile to return either an Array or a haxe.ds.GenericStack, and use either persons.sort(cmp) or ListSort.sortSingleLinked(persons.head, cmp).
Also, if necessary, you can easily convert any iterable – that is, any object that has an iterator:Void->Iterator<T> method – into an array with Lambda.array(iterable).
The documentation is lacking the necessary constraints on the T parameters. This is a bug in the documentation generator that I'll try to report soon.
From what I can see haxe.ds.ListSort is supposed to work on linked-list like structures, not Haxe Lists. If all you want to do is sort a list might be easier to simply use an Array. If your goal is to use this particular type of sorting and want to avoid using arrays (because of memory limits for example) you just need to provide it with a structure like:
typedef PersonListItem = {
var prev:PersonListItem;
var next:PersonListItem;
var person:Person;
}
(like the ListItem used internally by Haxe List actually)
But I assume you want to just sort "a list". So if that's what you are after it may look like this:
class Test {
static function main() {
var persons:Array<Person> = readPersonsFile("persons.txt");
trace(persons.join(","));
persons.sort(Person.compare);
trace(persons.join(","));
trace(persons[0]);
}
static function readPersonsFile(name:String):Array<Person> {
var result = new Array<Person>();
result.push(new Person(8));
result.push(new Person(1));
result.push(new Person(2));
result.push(new Person(6));
result.push(new Person(0));
result.push(new Person(9));
result.push(new Person(3));
result.push(new Person(7));
result.push(new Person(4));
result.push(new Person(5));
return result;
}
}
class Person {
var id:Int;
public function new(id) {
this.id = id;
}
public static function compare(a:Person, b:Person):Int {
return a.id - b.id;
}
public function toString():String {
return 'Person($id)';
}
}
Related
For example, consider the following C# code:
interface IBase { void f(int); }
interface IDerived : IBase { /* inherits f from IBase */ }
...
void SomeFunction()
{
IDerived o = ...;
o.f(5);
}
I know how to get a MethodDefinition object corresponding to SomeFunction.
I can then loop through MethodDefinition.Instructions:
var methodDef = GetMethodDefinitionOfSomeFunction();
foreach (var instruction in methodDef.Body.Instructions)
{
switch (instruction.Operand)
{
case MethodReference mr:
...
break;
}
yield return memberRef;
}
And this way I can find out that the method SomeFunction calls the function IBase.f
Now I would like to know the declared type of the object on which the function f is called, i.e. the declared type of o.
Inspecting mr.DeclaringType does not help, because it returns IBase.
This is what I have so far:
TypeReference typeRef = null;
if (instruction.OpCode == OpCodes.Callvirt)
{
// Identify the type of the object on which the call is being made.
var objInstruction = instruction;
if (instruction.Previous.OpCode == OpCodes.Tail)
{
objInstruction = instruction.Previous;
}
for (int i = mr.Parameters.Count; i >= 0; --i)
{
objInstruction = objInstruction.Previous;
}
if (objInstruction.OpCode == OpCodes.Ldloc_0 ||
objInstruction.OpCode == OpCodes.Ldloc_1 ||
objInstruction.OpCode == OpCodes.Ldloc_2 ||
objInstruction.OpCode == OpCodes.Ldloc_3)
{
var localIndex = objInstruction.OpCode.Op2 - OpCodes.Ldloc_0.Op2;
typeRef = locals[localIndex].VariableType;
}
else
{
switch (objInstruction.Operand)
{
case FieldDefinition fd:
typeRef = fd.DeclaringType;
break;
case VariableDefinition vd:
typeRef = vd.VariableType;
break;
}
}
}
where locals is methodDef.Body.Variables
But this is, of course, not enough, because the arguments to a function can be calls to other functions, like in f(g("hello")). It looks like the case above where I inspect previous instructions must repeat the actions of the virtual machine when it actually executes the code. I do not execute it, of course, but I need to recognize function calls and replace them and their arguments with their respective returns (even if placeholders). It looks like a major pain.
Is there a simpler way? Maybe there is something built-in already?
I am not aware of an easy way to achieve this.
The "easiest" way I can think of is to walk the stack and find where the reference used as the target of the call is pushed.
Basically, starting from the call instruction go back one instruction at a time taking into account how each one affects the stack; this way you can find the exact instruction that pushes the reference used as the target of the call (a long time ago I wrote something like that; you can use the code at https://github.com/lytico/db4o/blob/master/db4o.net/Db4oTool/Db4oTool/Core/StackAnalyzer.cs as inspiration).
You'll need also to consider scenarios in which the pushed reference is produced through a method/property; for example, SomeFunction().f(5). In this case you may need to evaluate that method to find out the actual type returned.
Keep in mind that you'll need to handle a lot of different cases; for example, imagine the code bellow:
class Utils
{
public static T Instantiate<T>() where T : new() => new T();
}
class SomeType
{
public void F(int i) {}
}
class Usage
{
static void Main()
{
var o = Utils.Instantiate<SomeType>();
o.F(1);
}
}
while walking the stack you'll find that o is the target of the method call; then you'll evaluate Instantiate<T>() method and will find that it returns new T() and knowing that T is SomeType in this case, that is the type you're looking for.
So the answer of Vagaus helped me come up with a working implementation.
I published it on github - https://github.com/MarkKharitonov/MonoCecilExtensions
Included many unit tests, but I am sure I missed some cases.
In python, I often use strings as templates, e.g.
templateUrl = '{host}/api/v3/{container}/{resourceid}'
params = {'host': 'www.api.com', 'container': 'books', 'resourceid': 10}
api.get(templateUrl.format(**params))
This allows for easy base class setup and the like. How can I do the same in dart?
I'm assuming I will need to create a utility function to parse the template and substitute manually but really hoping there is something ready to use.
Perhaps a TemplateString class with a format method that takes a Map of name/value pairs to substitute into the string.
Note: the objective is to have a generic "format" or "interpolation" function that doesn't need to know in advance what tags or names will exist in the template.
Further clarification: the templates themselves are not resolved when they are set up. Specifically, the template is defined in one place in the code and then used in many other places.
Dart does not have a generic template string functionality that would allow you to insert values into your template at runtime.
Dart only allows you to interpolate strings with variables using the $ syntax in strings, e.g. var string = '$domain/api/v3/${actions.get}'. You would need to have all the variables defined in your code beforehand.
However, you can easily create your own implementation.
Implementation
You pretty much explained how to do it in your question yourself: you pass a map and use it to have generic access to the parameters using the [] operator.
To convert the template string into something that is easy to access, I would simply create another List containing fixed components, like /api/v3/ and another Map that holds generic components with their name and their position in the template string.
class TemplateString {
final List<String> fixedComponents;
final Map<int, String> genericComponents;
int totalComponents;
TemplateString(String template)
: fixedComponents = <String>[],
genericComponents = <int, String>{},
totalComponents = 0 {
final List<String> components = template.split('{');
for (String component in components) {
if (component == '') continue; // If the template starts with "{", skip the first element.
final split = component.split('}');
if (split.length != 1) {
// The condition allows for template strings without parameters.
genericComponents[totalComponents] = split.first;
totalComponents++;
}
if (split.last != '') {
fixedComponents.add(split.last);
totalComponents++;
}
}
}
String format(Map<String, dynamic> params) {
String result = '';
int fixedComponent = 0;
for (int i = 0; i < totalComponents; i++) {
if (genericComponents.containsKey(i)) {
result += '${params[genericComponents[i]]}';
continue;
}
result += fixedComponents[fixedComponent++];
}
return result;
}
}
Here would be an example usage, I hope that the result is what you expected:
main() {
final templateUrl = TemplateString('{host}/api/v3/{container}/{resourceid}');
final params = <String, dynamic>{'host': 'www.api.com', 'container': 'books', 'resourceid': 10};
print(templateUrl.format(params)); // www.api.com/api/v3/books/10
}
Here it is as a Gist.
Here is my solution:
extension StringFormating on String {
String format(List<String> values) {
int index = 0;
return replaceAllMapped(new RegExp(r'{.*?}'), (_) {
final value = values[index];
index++;
return value;
});
}
String formatWithMap(Map<String, String> mappedValues) {
return replaceAllMapped(new RegExp(r'{(.*?)}'), (match) {
final mapped = mappedValues[match[1]];
if (mapped == null)
throw ArgumentError(
'$mappedValues does not contain the key "${match[1]}"');
return mapped;
});
}
}
This gives you a very similar functionality to what python offers:
"Test {} with {}!".format(["it", "foo"]);
"Test {a} with {b}!".formatWithMap({"a": "it", "b": "foo"})
both return "Test it with foo!"
It's even more easy in Dart. Sample code below :
String host = "www.api.com"
String container = "books"
int resourceId = 10
String templateUrl = "$host/api/v3/$container/${resourceId.toString()}"
With the map, you can do as follows :
Map<String, String> params = {'host': 'www.api.com', 'container': 'books', 'resourceid': 10}
String templateUrl = "${params['host']}/api/v3/${params['container']}/${params['resourceId']}"
Note : The above code defines Map as <String, String>. You might want <String, Dynamic> (and use .toString())
Wouldn't it be simplest to just make it a function with named arguments? You could add some input validation if you wanted to.
String templateUrl({String host = "", String container = "", int resourceid = 0 }) {
return "$host/api/v3/$container/$resourceId";
}
void main() {
api.get(templateUrl(host:"www.api.com", container:"books", resourceid:10));
}
I have a custom rest control written in Java. Everything works fine for string fields, but not for multi-value string fields. My code returns
"[Value1, Value2, Value3...]". Note there are no commas around the values. On the web page the output looks like this:
If I can get commas around the values, the front-end framework can easily parse it.
I have tried to parse the value from the field and to get it formatted correctly, but cannot seem to get it right.
The first set of code works for a string. The second is an attempt to work for a multi-value field.
Any help would be greatly appreciated.
writer.startProperty("chgTitle");
writer.outStringLiteral(String.valueOf(columnValues.get(0)));
writer.endProperty();
writer.startProperty("plpAffected");
Object tmpObj = columnValues.get(5);
if (tmpObj instanceof Vector) {
String[] copyArr = new String[((Vector) tmpObj).size()];
((Vector) tmpObj).copyInto(copyArr);
writer.outStringLiteral(String.valueOf(copyArr));
} else {
}
writer.endProperty();
I would recommend a slightly different approach. I like to force my JSON structures to use an array anywhere a multiple value situation is possible. It also looks like you're using Philippe Riand's specialized JSON writer, so I'll assume that.
Here's about how I would attack it:
writer.startProperty("chgTitle");
writer.outStringLiteral(String.valueOf(columnValues.get(0)));
writer.endProperty();
writer.startProperty("plpAffected");
Vector<?> tmpVec = Util.getValueAsVector(columnValues.get(5));
writer.startArray();
for ( Object ob : tmpVec ) {
writer.startArrayItem();
// assuming String contents
writer.outStringLiteral(String.valueOf(ob));
writer.endArrayItem();
}
writer.endArray();
writer.endProperty();
To wrap the returning columnValues, I'm using a Java equivalent of my SSJS getValueAsVector helper function. It checks for Vector or ArrayList, which I happen to use almost exclusively; if it's not, it shoves it into a new Vector. Here's what that method looks like,
public static Vector<?> getValueAsVector(Object obj) {
if(obj instanceof java.util.Vector){
return (Vector<?>) obj;
}else if( obj instanceof ArrayList ) {
List<?> o = (List<?>) obj;
Vector<Object> tmpVec = new Vector<Object>();
for(int i=0;i<o.size();i++){
tmpVec.add(o.get(i));
}
return tmpVec;
}else {
Vector<Object> tmpVec = new Vector<Object>();
tmpVec.add(obj);
return tmpVec;
}
}
I'm trying to make a Map with an object as a key. The problem is, that when I try to get elements from this map, I always get null. It's because I'm not providing the exact same reference as the key was. I'm providing an object with the same values, so the reference is different.
Is there any way to solve that? Can I make it use some kind of equals() function?
class PointInt
{
public var x:Int;
public var y:Int;
...
}
var map = new Map<PointInt, Hex>();
var a = new PointInt(1, 1);
var b = new PointInt(1, 1);
var hex_a = new Hex();
map[a] = hex_a;
var hex_b = map[b];
/// hex_b == null now because reference(a) == reference(b)
As explained here and here, Map in Haxe works using the reference of the object as the key.
What you want to use instead is a HashMap like this (try.haxe link):
import haxe.ds.HashMap;
class Test {
static function main() {
var map = new HashMap();
map.set(new PointInt(1, 1), 1);
trace(map.get(new PointInt(1,1)));
}
}
class PointInt
{
public var x:Int;
public var y:Int;
public function new(x:Int, y:Int)
{
this.x = x;
this.y = y;
}
public function hashCode():Int
{
return x + 1000*y; //of course don't use this, but a real hashing function
}
public function toString()
{
return '($x,$y)';
}
}
What you need to change in your code, besides using haxe.ds.HashMap instead of Map is to implement a hashCode : Void->Int function in your key object
Since you're using an object that has 2 ints, and the hash map is just 1 int, it will happen that 2 PointInt will have the same hash code. To solve this you could create a hash map that uses strings as hashcode but if you can write (or google) a good hash function you will get better performance.
This is an interesting error I've come across while implementing IEnumerable on a class. It appears to be similar to an "access to modified closure" issue, but I'm at a loss as to how to fix it.
Here is a simple example that demonstrates the issue:
void Main()
{
var nodeCollection = new NodeCollection();
nodeCollection.MyItems = new List<string>() { "a", "b", "c" };
foreach (var node in nodeCollection)
{
node.Dump();
}
}
public class NodeCollection : IEnumerable<Node>
{
public List<string> MyItems;
public IEnumerator<Node> GetEnumerator()
{
// This isn't necessary, but it should prove that it's not an "access to modified closure" issue.
var items = MyItems;
for (var i = 0; i < 3; i++)
{
var node = new Node();
// I want the node to contains the items in MyItems.
node.Items = items;
// Plus an additional item. Note that I am adding the item to the node, NOT to MyItems.
node.Items.Add(string.Format("iteration: {0}", i));
yield return node;
}
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
public class Node
{
public List<string> Items;
}
As you can see from the Dump() statement, I'm running this in LINQPad, but the issue will present itself in any IDE.
When I run the snippet, I get the following output:
Because I am adding the item to Items in the newly instantiated Node, I would NOT expect the item to be added to MyItems, but this is obviously what is occurring.
It seems that Items in Node is pointing to MyItems in NodeCollection.
Can anyone tell me:
Why this is happening?
How to make it not happen?
You are creating new nodes each iteration, but then setting the same items instance to the Items property of each node. Then you are adding the iteration string to the items instance stored in the Items collection (which is always the same instance), resulting in each subsequent node having more and more "iteration" entries. If you kept all of the nodes, you'd find that all of them have exactly the same Items value.
I think the basic misunderstanding here was that you were assuming that setting the Items property of the Node (node.Items = items;) would copy the items list into the node. In fact, all it does is set node.Items to point to the already-existing list that you call items.
This should give you an idea where you went wrong:
// This same instance of items is being reused each time
var items = MyItems;
for (var i = 0; i < 3; i++)
{
var node = new Node();
// I want the node to contains the items in MyItems.
// Assuming node.Items is a List<String>
node.Items = new List<String>();
node.Items.AddRange(items);
node.Items.Add(string.Format("iteration: {0}", i));
yield return node;
}
node.Items = items; sets node.Items to be a reference to the items list. There is just one list, with several references to it.
I suppose that what you want is to have a separate list in each node and that you want to copy the elements in items into that list. To do that, create a new list wich contains all of the elements from items.
node.Items = new List<string>(items);
When you do:
var item = MyItems;
you just create a reference to MyItems and store it in the variable item. Then when you do:
node.Items = items;
you just take the same reference and store it in node.Items. If you need node.Items to be a new list (point to a different memory location) initialize it again.
node.Items = new List();