Examples with int
Compiles without warnings with MSVC:
class A
{
public:
void f(const int a);
};
void A::f(int a)
{
a = 10;
std::cout << a;
}
error C3892: ‘a’: you cannot assign to a variable that is const:
class A
{
public:
void f(int a);
};
void A::f(const int a)
{
a = 10;
std::cout << a;
}
std::move and std::forward
We can’t make the parameters const if we move or forward them. For example, func parameter can’t be const in the code below:
template <size_t read_length, class Func>
requires std::invocable<Func, const boost::system::error_code&, std::size_t>
void asyncRead(uint8_t (&data)[read_length], Func&& func)
{
stream().async_read_some(
boost::asio::buffer(data, read_length),
std::forward<Func>(func));
}
Examples with a structure
This compiles without warnings with MSVC:
struct Value
{
int x;
std::string y;
};
class A
{
public:
void f(Value val);
};
void A::f(const Value val)
{
std::cout << val.x;
}
and there are no warnings either:
struct Value
{
int x;
std::string y;
};
class A
{
public:
void f(const Value val);
};
void A::f(Value val)
{
val.y = "abc";
std::cout << val.x << " " << val.y;
}
Automatic variables
We probably also make automatic variables const if we do not modify them.
