Examples of the different uses of const in C++

const_forms.cpp

#include <iostream>
#include <vector>
#include <string>
#include <memory>

typedef std::vector<std::string> str_vec;

void print(str_vec const list)
{
    for ( auto el : list ) std::cout << el << std::endl;
}

int main()
{
    // Immutable list of elements on the stack
    const str_vec names = {"one", "two"};
    // *(names.end() - 1) = "three";  // Compile error: immutable elements
    // names.push_back("three");  // Compile error: immutable list
    print(names);

    // Constant pointer to list of mutable elements
    //  Scala:  val name_ptr = Array("four", "five")
    const auto name_ptr = std::unique_ptr<str_vec>(new str_vec {"four","five"});
    (*name_ptr)[1]  = "six";  // OK
    print(*name_ptr);

    // Mutable pointer to list of immutable elements
    // Scala: var name_ptr2 = List("seven", "eight")
    auto name_ptr2 = std::unique_ptr<const str_vec>(new str_vec {"seven","eight"});
    // (*name_ptr2)[1] = "nine";  // Compile error: const elements
    print(*name_ptr2);
    //  Another list of immutable elements
    auto name_ptr3 = std::unique_ptr<const str_vec>(new str_vec {"nine","ten"});
    // Can reassign name_ptr2
    name_ptr2 = std::move(name_ptr3);  // OK
    print( *name_ptr2 );
    // print( *name_ptr3 ); // Runtime error: move deletes name_ptr3

    // Immutable pointer to list of immutable elements
    // Scala: val name_ptr4 = List("eleven")
    const auto name_ptr4 = std::unique_ptr<const str_vec>(new str_vec {"eleven"});
    // name_ptr4 = std::move(name_ptr2);  // Compile error: const pointer
    print( *name_ptr4 );

    return 0;
}