Difficulties to Assign Default Value to a Parameter of a Function

Difficulties to assign default value to a parameter of a function

I don't think that is possible. The default value is inserted at the calling site, and therefore needs to be public, see also
Access control in swift 4.

A possible workaround would be to make the parameter optional,
and substitute nil by the default value locally:

class Foo {
    private static let DefaultValue = 10

    public func doTask(amount: Int? = nil) {
        let amount = amount ?? Foo.DefaultValue
        // ...
    }
}

Problem with Functions which has default parameter(s)

1. Defaults arguments are bounds at function definition time. The line def Veli(a, b = my_list): puts a reference to the object my_list happens to refer to at that time into func_defaults. Python never uses pass-by-reference - variables hold references and those references are always passed by value. So what's actually saved in b, a reference (pointer), is copied and nobody remembers where it came from or bothers to update it.
2. Not quite sure what you're asking, please clarify. b will be Veli.func_defaults[0] if no second argument was passed, but obviously different if it is passed (well, unless of course the caller accesses func_defaults... you should assume he doesn't).You could, as suggested in another answer, make bdefault to None and use the global my_list if b is None - this would give you a fresh, updated copy of its reference on every call. Perhaps you should write a class and keep the default value as an attribute of self and apply the usual (... = None): if ... is None: use = default idiom.
3. The build-in function id. Actually, it's implementation defined what this returns (doesn't have to be the address), as long as it's an integer that represents the object identity, i.e. distinct objects (with overlapping lifetimes) have a distinct id and the same object always gives the same id during its lifetime. The easy return value, which CPython chooses, is the address.

How do I assign a default value to a function parameter that is a function? C++

Your parameter should be a pointer to a function, and you can assign this like any other parameter.

int Function3(int a, int b, int (*func)(int,int) = Function2)    
{
  func(a,b); //call will use passed function, or Function2 if one wasn't provided
}

Set a default parameter value for a JavaScript function

From ES6/ES2015, default parameters are in the language specification.

function read_file(file, delete_after = false) {
  // Code
}

just works.

Reference: Default Parameters - MDN

Default function parameters allow formal parameters to be initialized with default values if no value or undefined is passed.

In ES6, you can simulate default named parameters via destructuring:

// the `= {}` below lets you call the function without any parameters
function myFor({ start = 5, end = 1, step = -1 } = {}) { // (A)
    // Use the variables `start`, `end` and `step` here
    ···
}

// sample call using an object
myFor({ start: 3, end: 0 });

// also OK
myFor();
myFor({});

Pre ES2015,

There are a lot of ways, but this is my preferred method — it lets you pass in anything you want, including false or null. (typeof null == "object")

function foo(a, b) {
  a = typeof a !== 'undefined' ? a : 42;
  b = typeof b !== 'undefined' ? b : 'default_b';
  ...
}

How to assign default values to a function arguments at the run-time in C#

default parameters must be initialized with null or constant value.

public UpdateLocation(int? X = null, int? Y = null, int? Z = null)
{
    if(X.HasValue) this.X = X.Value;
    if(Y.HasValue) this.Y = Y.Value;
    if(Z.HasValue) this.Z = Z.Value;

    // this.X = X ?? this.X;
    // this.Y = Y ?? this.Y;
    // this.Z = Z ?? this.Z;
}

Now choose to update

UpdateLocation(Y: 5, X: 2);

Here you can read about named arguments.

problem in default argument in JavaScript's function

Eventhandler always give the event as an argument to the callback function. So this would not work. You can easily change your code to fulfill your requirements in this way

infoBtnCB.addEventListener("click", () => { clickEventInfoBtn_CB(); });
function clickEventInfoBtn_CB(remove = false) {
  console.log(remove);
  if (remove) {
    infoBtnCB.classList.remove("active-info-btn-CB");
  } else {
    infoBtnCB.classList.toggle("active-info-btn-CB");
  }
  if (infoBtnCB.innerHTML == "Info" && !remove) {
    setTimeout(() => {
      infoBtnCB.innerHTML =
        "Lorem ipsum dolor sit, amet consectetur adipisicing elit. Cumque accusamus ipsum, quidem harum similique blanditiis, veritatis nam sapiente tenetur rerum temporibus asperiores, commodi consequatur corporis quisquam aspernatur quas laudantium eaque.m";
    }, 100);
  } else {
    infoBtnCB.innerHTML = "Info";
  }
}

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