Challenge 2: A Class With an Explicitly Deleted Copy Constructor — Possible Solution
====================================================================

#include <iostream>

class NoCopy {
public:
    int value;
    NoCopy(int v) : value(v) {}
    NoCopy(const NoCopy &other) = delete;
};

int main() {
    NoCopy a(42);
    NoCopy b = a;  // compile error
    return 0;
}

Representative compile error:

    error: use of deleted function 'NoCopy::NoCopy(const NoCopy&)'
        NoCopy b = a;
                   ^
    note: 'NoCopy::NoCopy(const NoCopy&)' explicitly marked deleted here
        NoCopy(const NoCopy &other) = delete;
        ^

WHY THIS WORKS AS AN ANSWER
------------------------------
= delete explicitly marks the copy constructor as unusable -- per the
chapter, this is exactly the syntax cpp2-4's own unique_ptr uses
internally to enforce sole ownership. Attempting NoCopy b = a; still
compiles as far as syntax goes (it's ordinary copy-initialization) but
fails specifically because the ONE constructor that could satisfy it
has been explicitly deleted -- the compiler reports the exact deleted
function by name, rather than a generic type mismatch, confirming
= delete's intent is enforced as a hard compile-time error.