Is there any real reason to use "const"?

[rempas]

On Monday, 24 January 2022 at 11:15:47 UTC, Dennis wrote:
> 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.

I thought I tried it out some months ago and it wasn't possible. 
Well, turns out that I was wrong about the second part of my 
post. And that I'm an idiot of course but this is not something I 
didn't knew before neither something that will stop me....