Pass by const ref

[vladon]

cppbestpractices/04-Considering_Safety.md

Also, using const & prevents the compiler from copying data unnecessarily.

If you internally copy object to internal var, the better variant will be passing params by value.

First example marked as "Bad Idea":

// Bad Idea
//...
MyClass(std::string t_value)
    : m_value(t_value)
  {
  }
// ...
std::string m_value;

When you do m_value(t_value) in constructor initialization list, it is anyway will be a copy, it doesn't matter you pass it by const ref or by value.

But passing by value in such situations (when you copy contents to internal variable) is much more better: it is thread-safe, no dangling refs, you can pass rvalues, you can construct in-place, etc.

There will not be two copies, see copy elision.

So, in given example it is not a Bad Idea.

[lefticus]

I updated the example. We may want to address the copy/move idiom that some prefer for:

MyClass(std::string t_value)
  : m_value(std::move(t_value))
{
}

which an elide copies on r-values

But I'm not sure of I good place to put that and I know not everyone agrees with it.