Class constructor initializes and create objects/functions in a class. If I'm using functions, how would I initialize a function within the function?
This is the simple class
export default class MainProcess{
constructor() {
this.isReady = false
this.init()
}
init() {
this.setupApplicationMenu()
this.initWindowManager()
this.getIcons()
}
}
how can I initiate a MainPRocess Function?
While I'm not entirely sure I understand the question, I think you're asking "How can I create a function in a way that's similar to how I'm used to writing classes, but without using the class keyword?" Here's an example of that:
function Example () {
this.value = 10;
// instance method
this.print = function () {
console.log(this.value);
}
}
// static method
Example.printHello = function () {
console.log('hello world');
}
const example1 = new Example();
example1.print(); // 10
example1.value = 20;
example1.print(); //20
console.log(Object.getPrototypeOf(example1).constructor.name); // "Example"
const example2 = new Example();
example2. print(); //10
Example.printHello(); // "hello world"
Functions are part of the class. Classes are a grouping of functions(methods) and data(as properties). These functions are used to modify properties.
In the above example, you created a class MainProcess with some functions. However, functions defined in the init method is not present. The compiler will throw an error.
constructor is a special method used to create an object with that class.
If I'm using functions, how would I initialize a function within the
function?
It seems you are mixing two concepts function constructors in JS and Classes which are introduced later. Class is nothing, but a syntactic sugar on function constructor. JS is a prototype-based language.
difference b/w function and function constructor?
Functions created with the Function constructor do not create closures to their creation contexts; they always are created in the global scope. When running them, they will only be able to access their own local variables and global ones, not the ones from the scope in which the Function constructor was created. This is different from using Global_Objects/eval with code for a function expression.
var x = 10;
function createFunction1() {
var x = 20;
return new Function('return x;'); // this |x| refers global |x|
}
function createFunction2() {
var x = 20;
function f() {
return x; // this |x| refers local |x| above
}
return f;
}
var f1 = createFunction1();
console.log(f1()); // 10
var f2 = createFunction2();
console.log(f2()); // 20
I highly recommend you first understand the how JS has implemented class in it.
I am getting started with Haxe and OpenFl, and have some experience with Javascript and Lua.
It was going pretty well, till I got to a point where I needed a function similar to wait() in Lua, etc, which stops the script until the number of seconds you set is over.
How would I go about doing this?
EDIT: To clarify, I am building to Flash.
Although this is old, I wanted to add another point for reference. The OP mentioned in a comment this was for a game. One method I often use is (and could probably be put in a library):
var timerCount:Float = 0;
var maxTimerCounter:Float = 5;
function update () {
timerCounter += elapsedTime;
if (timerCounter > maxTimerCounter){
onTimerComplete();
timerCount = 0;
}
}
In SYS you are looking for:
static function sleep( seconds : Float ) : Void
Suspend the current execution for the given time (in seconds).
Example: Sys.sleep(.5);
http://haxe.org/api/sys/
Edit: User is porting to flash.
So the suggestion is to use Timer
http://haxe.org/api/haxe/timer
In Timer the suggestion is to use
static function delay( f : Void -> Void, time_ms : Int ) : Timer
Someone on stack overflow has an example that looks like this: haxe.Timer.delay(callback(someFunction,"abc"), 10); located here... Pass arguments to a delayed function with Haxe
For the Flash compile target, the best you can do is use a timer, and something like this setTimeout() function.
This means slicing your function into two - everything before the setTimeout(), and everything after that, which is in a separate function that the timeout can call.
so somethine like, eg:
tooltipTimerId = GlobalTimer.setTimeout(
Tooltip.TOOLTIP_DELAY_MS,
handleTooltipAppear,
tootipParams
);
[...]
class GlobalTimer {
private static var timerList:Array<Timer>;
public static function setTimeout(milliseconds:Int, func:Dynamic, args:Array<Dynamic>=null):Int {
var timer:Timer = new Timer(milliseconds);
var id = addTimer(timer, timerList);
timer.run = function() {
Reflect.callMethod(null, func, args);
clearTimeout(id);
}
return id;
}
private static function addTimer(timer:Timer, arr:Array<Timer>):Int {
for (i in 0...arr.length) {
if (null == arr[i]) {
arr[i] = timer;
return i;
}
}
arr.push(timer);
return arr.length -1;
}
public static function clearTimeout(id:Int) {
var timers:Array<Timer> = GlobalTimer.getInstance().timerList;
try {
timers[id].stop();
timers[id] = null;
} catch(e:Error) {/* Nothing we can do if it fails, really. */}
}
}
JavaScript allows functions to be treated as objects--if you first define a variable as a function, you can subsequently add properties to that function. How do you do the reverse, and add a function to an "object"?
This works:
var foo = function() { return 1; };
foo.baz = "qqqq";
At this point, foo() calls the function, and foo.baz has the value "qqqq".
However, if you do the property assignment part first, how do you subsequently assign a function to the variable?
var bar = { baz: "qqqq" };
What can I do now to arrange for bar.baz to have the value "qqqq" and bar() to call the function?
It's easy to be confused here, but you can't (easily or clearly or as far as I know) do what you want. Hopefully this will help clear things up.
First, every object in Javascript inherits from the Object object.
//these do the same thing
var foo = new Object();
var bar = {};
Second, functions ARE objects in Javascript. Specifically, they're a Function object. The Function object inherits from the Object object. Checkout the Function constructor
var foo = new Function();
var bar = function(){};
function baz(){};
Once you declare a variable to be an "Object" you can't (easily or clearly or as far as I know) convert it to a Function object. You'd need to declare a new Object of type Function (with the function constructor, assigning a variable an anonymous function etc.), and copy over any properties of methods from your old object.
Finally, anticipating a possible question, even once something is declared as a function, you can't (as far as I know) change the functionBody/source.
There doesn't appear to be a standard way to do it, but this works.
WHY however, is the question.
function functionize( obj , func )
{
out = func;
for( i in obj ){ out[i] = obj[i]; } ;
return out;
}
x = { a: 1, b: 2 };
x = functionize( x , function(){ return "hello world"; } );
x() ==> "hello world"
There is simply no other way to acheive this,
doing
x={}
x()
WILL return a "type error". because "x" is an "object" and you can't change it. its about as sensible as trying to do
x = 1
x[50] = 5
print x[50]
it won't work. 1 is an integer. integers don't have array methods. you can't make it.
Object types are functions and an object itself is a function instantiation.
alert([Array, Boolean, Date, Function, Number, Object, RegExp, String].join('\n\n'))
displays (in FireFox):
function Array() {
[native code]
}
function Boolean() {
[native code]
}
function Date() {
[native code]
}
function Function() {
[native code]
}
function Number() {
[native code]
}
function Object() {
[native code]
}
function RegExp() {
[native code]
}
function String() {
[native code]
}
In particular, note a Function object, function Function() { [native code] }, is defined as a recurrence relation (a recursive definition using itself).
Also, note that the answer 124402#124402 is incomplete regarding 1[50]=5. This DOES assign a property to a Number object and IS valid Javascript. Observe,
alert([
[].prop="a",
true.sna="fu",
(new Date()).tar="fu",
function(){}.fu="bar",
123[40]=4,
{}.forty=2,
/(?:)/.forty2="life",
"abc".def="ghi"
].join("\t"))
displays
a fu fu bar 4 2 life ghi
interpreting and executing correctly according to Javascript's "Rules of Engagement".
Of course there is always a wrinkle and manifest by =. An object is often "short-circuited" to its value instead of a full fledged entity when assigned to a variable. This is an issue with Boolean objects and boolean values.
Explicit object identification resolves this issue.
x=new Number(1); x[50]=5; alert(x[50]);
"Overloading" is quite a legitimate Javascript exercise and explicitly endorsed with mechanisms like prototyping though code obfuscation can be a hazard.
Final note:
alert( 123 . x = "not" );
alert( (123). x = "Yes!" ); /* ()'s elevate to full object status */
Use a temporary variable:
var xxx = function()...
then copy all the properties from the original object:
for (var p in bar) { xxx[p] = bar[p]; }
finally reassign the new function with the old properties to the original variable:
bar = xxx;
var A = function(foo) {
var B = function() {
return A.prototype.constructor.apply(B, arguments);
};
B.prototype = A.prototype;
return B;
};
NB: Post written in the style of how I solved the issue. I'm not 100% sure it is usable in the OP's case.
I found this post while looking for a way to convert objects created on the server and delivered to the client by JSON / ajax.
Which effectively left me in the same situation as the OP, an object that I wanted to be convert into a function so as to be able to create instances of it on the client.
In the end I came up with this, which is working (so far at least):
var parentObj = {}
parentObj.createFunc = function (model)
{
// allow it to be instantiated
parentObj[model._type] = function()
{
return (function (model)
{
// jQuery used to clone the model
var that = $.extend(true, null, model);
return that;
})(model);
}
}
Which can then be used like:
var data = { _type: "Example", foo: "bar" };
parentObject.createFunc(data);
var instance = new parentObject.Example();
In my case I actually wanted to have functions associated with the resulting object instances, and also be able to pass in parameters at the time of instantiating it.
So my code was:
var parentObj = {};
// base model contains client only stuff
parentObj.baseModel =
{
parameter1: null,
parameter2: null,
parameterN: null,
func1: function ()
{
return this.parameter2;
},
func2: function (inParams)
{
return this._variable2;
}
}
// create a troop type
parentObj.createModel = function (data)
{
var model = $.extend({}, parentObj.baseModel, data);
// allow it to be instantiated
parentObj[model._type] = function(parameter1, parameter2, parameterN)
{
return (function (model)
{
var that = $.extend(true, null, model);
that.parameter1 = parameter1;
that.parameter2 = parameter2;
that.parameterN = parameterN;
return that;
})(model);
}
}
And was called thus:
// models received from an AJAX call
var models = [
{ _type="Foo", _variable1: "FooVal", _variable2: "FooVal" },
{ _type="Bar", _variable1: "BarVal", _variable2: "BarVal" },
{ _type="FooBar", _variable1: "FooBarVal", _variable2: "FooBarVal" }
];
for(var i = 0; i < models.length; i++)
{
parentObj.createFunc(models[i]);
}
And then they can be used:
var test1 = new parentObj.Foo(1,2,3);
var test2 = new parentObj.Bar("a","b","c");
var test3 = new parentObj.FooBar("x","y","z");
// test1.parameter1 == 1
// test1._variable1 == "FooVal"
// test1.func1() == 2
// test2.parameter2 == "a"
// test2._variable2 == "BarVal"
// test2.func2() == "BarVal"
// etc
Here's easiest way to do this that I've found:
let bar = { baz: "qqqq" };
bar = Object.assign(() => console.log("do something"), bar)
This uses Object.assign to concisely make copies of all the the properties of bar onto a function.
Alternatively you could use some proxy magic.
JavaScript allows functions to be
treated as objects--you can add a
property to a function. How do you do
the reverse, and add a function to an
object?
You appear to be a bit confused. Functions, in JavaScript, are objects. And variables are variable. You wouldn't expect this to work:
var three = 3;
three = 4;
assert(three === 3);
...so why would you expect that assigning a function to your variable would somehow preserve its previous value? Perhaps some annotations will clarify things for you:
// assigns an anonymous function to the variable "foo"
var foo = function() { return 1; };
// assigns a string to the property "baz" on the object
// referenced by "foo" (which, in this case, happens to be a function)
foo.baz = "qqqq";
var bar = {
baz: "qqqq",
runFunc: function() {
return 1;
}
};
alert(bar.baz); // should produce qqqq
alert(bar.runFunc()); // should produce 1
I think you're looking for this.
can also be written like this:
function Bar() {
this.baz = "qqqq";
this.runFunc = function() {
return 1;
}
}
nBar = new Bar();
alert(nBar.baz); // should produce qqqq
alert(nBar.runFunc()); // should produce 1
I'm trying to pass a Class reference and instantiate it in a function. This doesn't work:
function foo(myClassRef:Class):Void {
var myVar = new myClassRef();
}
foo(MyClass);
It gives Unexpected (.
Is this possible in Haxe 3?
Class has a Type Parameter, so if you're going to accept a class as an argument, you need to specify a type parameter.
Accept any class:
function foo(myClassRef:Class<Dynamic>):Void {
var myVar = Type.createInstance( myClassRef, [constructorArg1, constructorArg2....] );
trace( Type.typeof(myVar) );
}
Accept only "sys.db.Object" class or sub classes:
function foo(myClassRef:Class<sys.db.Object>):Void {
var myVar = Type.createInstance( myClassRef, [] );
trace( Type.typeof(myVar) );
}
Haxe 3 also allows generic functions:
#:generic function foo<T:Dynamic>(t:Class<T>) {
var myVar = new T();
trace( Type.typeof(myVar) );
}
Here you declare the function to be generic, which means that for each different type parameter, a different version of the function will be compiled. You accept Class, where T is the type parameter - in this case, dynamic, so it will work with any class. Finally, using generic functions let's you write new T(), which may seem a more natural syntax, and there may be performance benefits on some platforms.
It is possible in Haxe3 and Haxe2
function foo<T>(myClassRef:T):Void {
var myVar = new T();
}
Note: Haxe3 class (where foo is implemented) must be #:generic if you want new T() to work.
Haxe2 is another story:
function foo<T>(myClassRef:Class<T>):Void {
var myVar = Type.createEmptyInstance(Type.getClass(myClassRef));
}
I would like to see a simple example of how to override stdext::hash_compare properly, in order to define a new hash function and comparison operator for my own user-defined type. I'm using Visual C++ (2008).
This is how you can do it
class MyClass_Hasher {
const size_t bucket_size = 10; // mean bucket size that the container should try not to exceed
const size_t min_buckets = (1 << 10); // minimum number of buckets, power of 2, >0
MyClass_Hasher() {
// should be default-constructible
}
size_t operator()(const MyClass &key) {
size_t hash_value;
// do fancy stuff here with hash_value
// to create the hash value. There's no specific
// requirement on the value.
return hash_value;
}
bool operator()(const MyClass &left, const MyClass &right) {
// this should implement a total ordering on MyClass, that is
// it should return true if "left" precedes "right" in the ordering
}
};
Then, you can just use
stdext::hash_map my_map<MyClass, MyValue, MyClass_Hasher>
Here you go, example from MSDN
I prefer using a non-member function.
The method expained in the Boost documentation article Extending boost::hash for a custom data type seems to work.