Passing the action name having return type to EOSIO_DISPATCH in EOSIO smart contract

Question

I have following EOSIO smart contract:

#include <eosiolib/eosio.hpp>
#include <eosiolib/print.hpp>

using namespace eosio;

class random : public contract
{
public:
  using contract::contract;

  [[eosio::action]]
  void hi(name user) {
    print("Hello and welcome to the future ", user);
  }
  [[eosio::action]]
  int compute(int x)
  {
    // unsigned means no negative values which increases the range of numbers the variable can hold
    const unsigned int FIVE = 5;
    // FIVE = 3; // would throw an error as FIVE is declared constant
    return x * x + FIVE;
  }
};

EOSIO_DISPATCH(random, (compute))

I am not getting how to call compute action in EOSIO_DISPATCH(random, (compute)) because it has return type int. Can somebody help me with this? I want to deploy this smart contract on testnet. Following error is generated when I execute eosio-cpp -o random.wasm random.cpp --abigen:

random.cpp:62:1: error: no matching function for call to 'execute_action'
EOSIO_DISPATCH(random, (compute))
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/eosio.cdt/bin/../include/eosiolib/dispatcher.hpp:128:13: note: expanded from macro 'EOSIO_DISPATCH'
            EOSIO_DISPATCH_HELPER( TYPE, MEMBERS ) \
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/eosio.cdt/bin/../include/eosiolib/dispatcher.hpp:103:27: note: expanded from macro 'EOSIO_DISPATCH_HELPER'
   BOOST_PP_SEQ_FOR_EACH( EOSIO_DISPATCH_INTERNAL, TYPE, MEMBERS )
   ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/eosio.cdt/bin/../include/boost/preprocessor/seq/for_each.hpp:29:88: note: expanded from macro 'BOOST_PP_SEQ_FOR_EACH'
#    define BOOST_PP_SEQ_FOR_EACH(macro, data, seq) BOOST_PP_SEQ_FOR_EACH_DETAIL_CHECK(macro, data, seq)
                                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
note: (skipping 6 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
/usr/local/eosio.cdt/bin/../include/boost/preprocessor/seq/for_each.hpp:78:76: note: expanded from macro 'BOOST_PP_SEQ_FOR_EACH_M_IM'
#    define BOOST_PP_SEQ_FOR_EACH_M_IM(r, im) BOOST_PP_SEQ_FOR_EACH_M_I(r, im)
                                              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
/usr/local/eosio.cdt/bin/../include/boost/preprocessor/seq/for_each.hpp:83:61: note: expanded from macro 'BOOST_PP_SEQ_FOR_EACH_M_I'
# define BOOST_PP_SEQ_FOR_EACH_M_I(r, macro, data, seq, sz) macro(r, data, BOOST_PP_SEQ_HEAD(seq))
                                                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/eosio.cdt/bin/../include/eosiolib/dispatcher.hpp:98:7: note: expanded from macro 'EOSIO_DISPATCH_INTERNAL'
      eosio::execute_action( eosio::name(receiver), eosio::name(code), &OP::elem ); \
      ^~~~~~~~~~~~~~~~~~~~~
/usr/local/eosio.cdt/bin/../include/eosiolib/dispatcher.hpp:66:9: note: candidate template ignored: could not match 'void' against 'int'
   bool execute_action( name self, name code, void (T::*func)(Args...)  ) {
        ^
1 error generated.

Answer 1

There is some of the modification required in your contract to compile it.

#include <eosiolib/eosio.hpp>
#include <eosiolib/print.hpp>

using namespace eosio;

 class [[eosio::contract("random")]] random : public contract
{
  public:
  using contract::contract;

  [[eosio::action]]
  void hi(name user) {
    print("Hello and welcome to the future ", user);
  }
  [[eosio::action]]
  void compute(int x)
  {
    // unsigned means no negative values which increases the range of numbers the variable can hold
    const unsigned int FIVE = 5;
    // FIVE = 3; // would throw an error as FIVE is declared constant
    print( x * x + FIVE);
  }
};

EOSIO_DISPATCH(random, (compute))

And for query regarding return type have a look at this discussion and this.