Elaboration on Herb Sutter Core Guidlines example for Smart Pointers (See 57:45 into https://youtu.be/hEx5DNLWGgA)

Cpp_Core_Guidline_R37_Herb_Sutter_CppCon2015_Example.cpp

//
//  main.cpp
//  MySharedPtrPlayGround
//
//  Created by Kjell-Olov Högdahl on 2016-08-15.
//  Copyright © 2016 Kjell-Olov Högdahl. All rights reserved.
//

#include <iostream>
#include <memory> // shared_ptr

// Elaboration on Herb Sutter Core Guidlines example for Smart Pointers (See 57:45 into https://youtu.be/hEx5DNLWGgA)

auto gsp = std::make_shared<int>();
void f(int* p) {
    // Mutate globally accessible owner
    gsp.reset();    // (1) If called with f(gsp.get()) gsp.reset() will invalidate existence of *p
                    // (2) If called with f(sp.get()) gsp.reset() will NOT invalidate existence of *p.
    *p = 4;         // Ok as long as *p is not owned by global gsp.
}

void g(std::shared_ptr<int>& sp,int* p) {
    // Mutate passed non-const owner
    sp.reset(); // (3) if called with g(sp_x,sp_x.get()) (sp_x some shared pointer) sp.reset() will invalidate existence of *p.
                // (4) If called with (sp_x, sp_y.get()) (sp_x and sp_y shared pointers owning different objects) sp.reset will NOT invalidate existence of *p.
    *p = 4;     // Ok as long as *p is not owned by passed sp
}

int main(int argc, const char * argv[]) {

    // See "R.37: Do not pass a pointer or reference obtained from an aliased smart pointer" at (https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines.html#a-namerr-smartptrgetar37-do-not-pass-a-pointer-or-reference-obtained-from-an-aliased-smart-pointer)
    
    f(gsp.get());       // (1) Error: f may invalidate existence of accessible *p (*gsp.get()) e.g., by calling gsp.reset()
                        // Hint: gsp is in global scope and thus accessible by f.
                        // ==> So don't pass raw pointer or reference to global scope owned object
    auto sp = gsp;      // Pin existence of gsp owned object to this stack
    f(sp.get());        // (2) OK. sp keeps int owned by gsp alive while call to f.
    g(gsp,gsp.get());   // (3) Error: g may invalidate existence of accessible *p (*gsp.get()) e.g., by sp.reset().
                        // Hint: g gets gsp access by non-const reference parameter sp.
                        // ==> So don't pass mutable owner to g of objects used by g.
    g(gsp, sp.get());   // (4) Ok. Inside g *p will exist during whole call whatever g does with passed or global owners
    return 0;
}