C++ Const-ness Noodle
We have been working with Javascript at the day job. I found it odd that const x = {a:1,b:2} did not make the value of the object immutable. I found it even more odd that Javascript has Object.freeze() which does make the value immutable. Why is that not the default when declaring const x?
This prompted me to revisit Good Ole C++ to see if my recollection of const-ness there was accurate. It is.
Here’s a snippet that you can paste into Compiler Explorer to show it for the simple case of a struct.
#include <vector>
#include <iostream>
int main() {
typedef struct T { int a; int b;} T;
T x = {1,2};
const T y = {3,4};
T* px = &x;
// T* py = &y; //error, cannot assign const y to non-const
const T* cpx = &x;
const T* cpy = &y;
const T* const cpcx = &x;
const T* const cpcy = &y;
T& rx = x;
// T& ry = y; //error, cannot assign const y to non-const
const T& crx = x;
const T& cry = y;
std::cout << x.a << x.b
<< y.a << y.b
<< px->a << px->b
// << py->a << py->b
<< cpx->a << cpx->b
<< cpy->a << cpy->b
<< cpcx->a << cpcx->b
<< cpcy->a << cpcy->b
<< rx.a << rx.b
// << ry.a << ry.b
<< crx.a << crx.b
<< cry.a << cry.b
;
x.a = 42;
// y.a = 42; //error
px->a = 42;
// py->a = 42; //error
// cpx->a = 42; //error
// cpy->a = 42; //error
// cpcx->a = 42; //error
// cpcy->a = 42; //error
rx.a = 42;
// ry.a = 42;
// crx.a = 42; // error
// cry.a = 42; //error
}