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  • Class member encapsulation

Class member encapsulation

# monolithed (9 years ago)

C++:

#include <iostream>

class A {
	public:
		A () {
   			this->x = 1;
		}

   		int call () {
   			return this->x;
   		}

		int x;
};

class B : public A {
	public:
		B() : A () {
			this->x = 2;
		}

		int x;
};


int main () {
	B b;

	std::cout << b.call(); // 1
	
	return 0;
}

JavaScript:

class A {
   constructor () {
      this.x = 1;
   }

   call () {
      return this.x;
   }
}


class B extends A {
   constructor () {
      super();
      this.x = 2;
   }
}


let b = new B();

b.call(); // 2

Why we have different behavior?! I know that ECMAScript classes are syntactical sugar, but this behavior is unexpected for many people...

# Brendan Eich (9 years ago)

C++ has static inheritance and typing. this->A::x is 1 after B's

constructor delegates to A's constructor, and this->B::x (a different

field) is 2 once that field has been set in B::B.

JS has (not yet, anyway) no field declarations, no namespacing akin to A::x and B::x, and so only one this.x to mutate among the super and subclass when constructing a new instance of b.

JS ain't C++, no one has ever accused it of that (or me of "making it into C++", lol).

# Claude Pache (9 years ago)

Le 4 janv. 2016 à 00:07, monolithed <monolithed at gmail.com> a écrit :

Why we have different behavior?! I know that ECMAScript classes are syntactical sugar, but this behavior is unexpected for many people...

The C++ behaviour indeed surprises me, but this mailing list is not exactly for discussing C++ class semantics. ;-) Also, "ECMAScript classes are syntactical sugar" is not an argument for discrepancy (and it is incorrect, anyway).