Are the days of passing const std::string & as a parameter over?

Question

I heard a recent talk by Herb Sutter who suggested that the reasons to pass std::vector and std::string by const & are largely gon

Answer 1

Short answer: NO! Long answer:

• If you won't modify the string (treat is as read-only), pass it as const ref&.
  (the const ref& obviously needs to stay within scope while the function that uses it executes)
• If you plan to modify it or you know it will get out of scope (threads), pass it as a value, don't copy the const ref& inside your function body.

There was a post on cpp-next.com called "Want speed, pass by value!". The TL;DR:

Guideline: Don’t copy your function arguments. Instead, pass them by value and let the compiler do the copying.

TRANSLATION of ^

Don’t copy your function arguments --- means: if you plan to modify the argument value by copying it to an internal variable, just use a value argument instead.

So, don't do this:

std::string function(const std::string& aString){
    auto vString(aString);
    vString.clear();
    return vString;
}

do this:

std::string function(std::string aString){
    aString.clear();
    return aString;
}

When you need to modify the argument value in your function body.

You just need to be aware how you plan to use the argument in the function body. Read-only or NOT... and if it sticks within scope.