Is there any real reason to use "const"?

[Dennis]

On Monday, 24 January 2022 at 10:06:49 UTC, rempas wrote:
> For example, you cannot past "const" variables to functions 
> that take non-const parameters even if we are using variables 
> which are ALWAYS copied (which means than modifying them will 
> not modify the original value).

You can? This compiles:
```D
struct S {
     int x;
     const(int)[] arr;
     immutable(char)[] str;
}

void main() {
     const S sc;
     immutable S si;
     f(sc); // mutable copy passed to f
     f(si); // mutable copy passed to f
}

void f(S s) {
     s.x = 3;
}
```
It will only error if the type has mutable indirections, because 
then you could violate `const` by changing the contents behind 
the array/pointer.