Some comments

[uselessgoddess]

• use C++ type style:
  - Type& val
  - Type* val
• use std::move for forward std::string (and other big [not fundamental] types)

  constructor(std::string string)
      : field(std::move(string)) 

• use const & for [big type] argument
• use universal reference to forward template argument
• use std::forward to forward template argument

auto function(std::vector<big_type>& list, big_type case1, const big_type& case2, auto&& case3)
{
    list.push_back(std::move(case1)) // one copy/only move, but call function(list, std::move(val), ..., ...)
    list.push_back(case2) // always one copy
    list.push_back(std::forward<decltype(case3)>(case3)) // same case1 but have other features
}

auto function(big_type case1, const big_type& case2, auto&& case3)
{
    case1.readonly_func() // (( always one copy 
    case2.readonly_func() // )) no copy
    case3.readonly_func() // )) no copy
}