Compact way to write if(..) statement with many equalities

Question

Is there a better way to write code like this:

if (var == "first case" or var == "second case" or var == "third case" or ...) 

In Python I can write:

if var in ("first case", "second case", "third case", ...) 

which also gives me the opportunity to easily pass the list of good options:

good_values = "first case", "second case", "third case" if var in good_values 

This is just an example: the type of var may be different from a string, but I am only interested in alternative (or) comparisons (==). var may be non-const, while the list of options is known at compile time.

Pro bonus:

• laziness of or
• compile time loop unrolling
• easy to extend to other operators than ==

Answer 1

if you want to expand it compile time you can use something like this

template<class T1, class T2> bool isin(T1&& t1, T2&& t2) {    return t1 == t2; }  template<class T1, class T2, class... Ts> bool isin(T1&& t1 , T2&& t2, T2&&... ts) {    return t1 == t2 || isin(t1, ts...); }  std::string my_var = ...; // somewhere in the code ... bool b = isin(my_var, "fun", "gun", "hun"); 

I did not test it actually, and the idea comes from Alexandrescu's 'Variadic templates are funadic' talk. So for the details (and proper implementation) watch that.

Edit: in c++17 they introduced a nice fold expression syntax

template<typename... Args> bool all(Args... args) { return (... && args); }  bool b = all(true, true, true, false);  // within all(), the unary left fold expands as  //  return ((true && true) && true) && false;  // b is false