how to delete a particular json element by variable:
i.e. I want to delete obj.a.b, but it is passed by a variable.
Is there a simple way to implement this?
var t = 'obj.a.b';
var obj = {a: {b: 'b', b2: 'b2'}};
delete t; // not work here
console.log(JSON.stringify(obj));
If you trust the value of t, you can use the eval(...) function to execute dynamic code like this:
var t = 'obj.a.b';
var obj = {a: {b: 'b', b2: 'b2'}};
eval("delete " + t + ";");
console.log(JSON.stringify(obj));
Note that if you cannot trust the value of t (e.g. it's a user-supplied value), an attacker can inject code by supplying a malicious value for t. You have to use eval(...) carefully as it can easily lead to such code-injection attack. This answer has good discussion about how and when to use eval.
Related
Say I have a two classes and a procedure that modifies either class in the same manner. How do I specify that a parameter can be either class (instead of rewriting or overloading the function for each class)? A simple example:
type
Class1[T] = object
x: T
Class2[T] = object
x: T
y: T
# this works fine
proc echoX[T](c: Class1[T]|Class2[T]) =
echo c.x
# this does not work
proc addToX[T](c: var Class1[T]|Class2[T], val: T) =
c.x += val
var c1: Class1[int]
var c2: Class2[int]
# this works fine
echoX(c1)
echoX(c2)
# this does not work
addToX(c1, 10)
addToX(c2, 100)
I get the following error.
Error: for a 'var' type a variable needs to be passed
If I use a separate procedure for each class, things work fine.
proc addToX[T](c: var Class1[T], val: T) =
c.x += val
proc addToX[T](c: var Class2[T], val: T) =
c.x += val
This is just a simple example where it's easy to rewrite the function. But I'm looking to do this for more complex classes and procedures. In some cases inheritance might be appropriate, but it doesn't seem like Nim classes can be passed as variables to procedures in place of the base class.
A bracket fixes this problem, otherwise the var just applies to Class1[T]:
proc addToX[T](c: var (Class1[T]|Class2[T]), val: T) =
You may run into another compiler bug with this later: https://github.com/nim-lang/Nim/issues/1385
Maybe in your use case object variantes or inheritance and methods will work better.
My goal is to create some kind of Parser to parse string formulas, similar to Excel formulas.
Formula string example (barcode example) -
"CONCAT('98', ZEROFILL([productNumber],5,'0'), ZEROFILL(EQUATION([weightKG]*1000),5,'0'))"
where
'98' - String
[productNumber] and [weightKG] - are variables that can be changed
CONCAT, ZEROFILL and EQUATION are methods which exist in class
For this formula with variables [productNumber] = '1' and [weightKG] = 0.1 result must be
'980000100100'
The question is how to split/parse whole string to parts and detect methods, variables and string values?
Another idea occurred, while i was typing - is to store whole formula in XML format.
Thank You.
You can use String.split() to get an array of substrings.
However, using your example, calling split(",") would give you the following array:
[0]=CONCAT('98'
[1]= ZEROFILL([productNumber]
[2]=5
[3]='0')
[4]= ZEROFILL(EQUATION([weightKG]*1000)
[5]=5
[6]='0'))
That doesn't seem like it will be very helpful for your project. Instead, you might think about creating a parse() function with some logic to find useful substrings:
function parse(input:String):Array {
var firstParen:int = input.indexOf("(");
var lastParen:int = input.lastIndexOf(")");
var formulaName:String = input.substring(0, firstParen);
var arguments:String = input.substring(firstParen, lastParen);
var argumentList:Array = parseArgs(arguments);
var result:Array = new Array();
result.push(formulaName);
//Recursively call parse() on the argumentList
foreach (var elem:* in argumentList) {
result.push(elem); //Could be string or array.
}
}
function parseArgs(input:String):Array {
// Look for commas that aren't enclosed inside parenthesis and
// construct an array of substrings based on that.
//A regex may be helpful here, but the implementation is left
//as an exercise for the reader.
}
The realtime api documentation indicates that the set method of CollaborativeMap should return the previous value at the given key, if there is one. Instead, it seems to return some object that has the old value as a property.
var map = doc.getModel().createMap();
map.set('key', 'val');
var oldValue = map.set('key', 'val2');
console.log(oldValue === 'val1'); // false
console.log(oldValue); // Tm {a: ""val"", Pa: Object, K: function, pa: function, J: function…}
It looks like an internal data structure in the Realtime API is being returned instead of the intended value. Thanks for reporting this issue - we're looking into it.
I will run a set of experiments. The main method evaluated has the following signature:
[Model threshold] = detect(...
TrainNeg, TrainPos, nf, nT, factors, ...
removeEachStage, applyEstEachStage, removeFeatures);
where removeEachStage, applyEstEachStage, and removeFeatures are booleans. You can see that if I reverse the order of any of these boolean parameters I may get wrong results.
Is there a method in MATLAB that allows better organization in order to minimize this kind of error? Or is there any tool I can use to protect me against these errors?
Organization with a struct
You could input a struct that has these parameters as it's fields.
For example a structure with fields
setts.TrainNeg
.TrainPos
.nf
.nT
.factors
.removeEachStage
.applyEstEachStage
.removeFeatures
That way when you set the fields it is clear what the field is, unlike a function call where you have to remember the order of the parameters.
Then your function call becomes
[Model threshold] = detect(setts);
and your function definition would be something like
function [model, threshold] = detect(setts)
Then simply replace the occurrences of e.g. param with setts.param.
Mixed approach
You can also mix this approach with your current one if you prefer, e.g.
[Model threshold] = detect(in1, in2, setts);
if you wanted to still explicitly include in1 and in2, and bundle the rest into setts.
OOP approach
Another option is to turn detect into a class. The benefit to this is that a detect object would then have member variables with fixed names, as opposed to structs where if you make a typo when setting a field you just create a new field with the misspelled name.
For example
classdef detect()
properties
TrainNeg = [];
TrainPos = [];
nf = [];
nT = [];
factors = [];
removeEachStage = [];
applyEstEachStage = [];
removeFeatures =[];
end
methods
function run(self)
% Put the old detect code in here, use e.g. self.TrainNeg to access member variables (aka properties)
end
end
From what I understand of ActionScript, there are two kinds of casts:
var bar0:Bar = someObj as Bar; // "as" casting
var bar1:Bar = Bar(someObj); // "class name" casting (for want of a better name)
Also, and please correct me if I'm wrong here, as casting will either return an instance of the class or null, while "class name" casting will either return an instance of the class or raise an exception if the cast is impossible – other than this, they are identical.
Given this, though, as casting seems to be a massive violation of the fail-fast-fail-early principle... And I'm having trouble imagining a situation where it would be preferable to use an as cast rather than a class name cast (with, possibly, an instanceof thrown in there).
So, my question is: under what circumstances would it be preferable to use as casting?
There are a couple of points in this discussion worth noting.
There is a major difference in how the two work, Class() will attempt to cast the object to the specified Class, but on failure to do so will (sometimes, depends on datatype) throw a runtime error. On the other hand using object as Class will preform a type check first, and if the specified object cannot be cast to the indicated Class a null value is returned instead.
This is a very important difference, and is a useful tool in development. It allows us to do the following:
var o:MyClass = myArray[i] as MyClass;
if(o)
{
//do stuff
}
I think the usefulness of that is pretty obvious.
"as" is also more consistent with the rest of the language (ie: "myObject is MyClass").
The MyClass() method has additional benefits when working with simple data types (int, Number, uint, string) Some examples of this are:
var s:String = "89567";
var s2:String = "89 cat";
var n:Number = 1.9897;
var i:int = int(s); // i is = 89567, cast works
var i2:int = int(s2); //Can't convert so i2 is set to 0
var i3:int = int(n); // i = 1
var n2:Number = Number(s2); // fails, n2 = NaN
//when used in equations you'll get very different results
var result:int = int(n) * 10; //result is 10
var result:int = n * 10; //result is 19.89700
var result:int = int(s2) * 10; //result is 0
trace(s2 as Number); //outputs null
trace(s2 as int); //outputs null
trace(Number(s2)); //outputs NaN
This is a good and important topic, as a general rule I use "as" when working with Objects and Cast() when using simpler data types, but that's just how I like to structure my code.
You need to use as to cast in two scenarios: casting to a Date, and casting to an Array.
For dates, a call to Date(xxx) behaves the same as new Date().toString().
For arrays, a call to Array(xxx) will create an Array with one element: xxx.
The Class() casting method has been shown to be faster than as casting, so it may be preferable to as when efficiency matters (and when not working with Dates and Arrays).
import flash.utils.*;
var d = Date( 1 );
trace( "'" + d, "'is type of: ",getQualifiedClassName( d ) );
var a:Array = Array( d );
trace( "'" + a, "' is type of: ", getQualifiedClassName( a ) );
//OUTPUT
//'Mon Jun 15 12:12:14 GMT-0400 2009 'is type of: String
//'Mon Jun 15 12:12:14 GMT-0400 2009 ' is type of: Array
//COMPILER ERRORS/WARNINGS:
//Warning: 3575: Date(x) behaves the same as new Date().toString().
//To cast a value to type Date use "x as Date" instead of Date(x).
//Warning: 1112: Array(x) behaves the same as new Array(x).
//To cast a value to type Array use the expression x as Array instead of Array(x).
`
They actually do different things...when you say
myvar as ClassName
You are really just letting the compiler know that this object is either a ClassName or a subclass of ClassName
when you say:
ClassName(myvar)
It actually tries to convert it to that type of object.
so if your object is a or a descent of the class and you do not need to convert it you would use as
examples:
var myvar:String = '<data/>';
var othervar:XML = XML(myvar); //right
var myvar:String = '<data/>';
var othervar:XML = (myvar as XML); //wrong
var myvar:XML = <data/>;
var othervar:XML = myvar as XML; // right
Use 'as' with arrays.
var badArray:Array;
badArray = Array(obj);
Will yield an array of length one with the original array in the first element. If you use 'as' as follows, you get the exptected result.
var goodArray:Array;
goodArray = obj as Array;
Generally, 'as' is preferable to 'Class()' in ActionScript as it behaves more like casting in other languages.
I use it when I have an ArrayCollection of objects and need to enumerate through them, or use a selector function.
e.g.
var abc:mytype = mycollection.getItemAt(i) as mytype