Let’s build a game using EOS, and what better game to create than rock-paper-scissors? We’ve already covered EOS in a previous example, so now it’s time to put that knowledge into practice.
// rock-paper-scissors game in EOS
#include <eosiolib/eosio.hpp>
#include <eosiolib/print.hpp>
using namespace eosio;
class rps : public contract {
public:
using contract::contract;
[[eosio::action]]
void play(name player1, name player2, std::string choice1, std::string choice2) {
require_auth(player1);
require_auth(player2);
eosio_assert(choice1 == "rock" || choice1 == "paper" || choice1 == "scissors", "Invalid choice1");
eosio_assert(choice2 == "rock" || choice2 == "paper" || choice2 == "scissors", "Invalid choice2");
game_index games(_self, _self.value);
games.emplace(player1, [&](auto& g) {
g.key = games.available_primary_key();
g.player1 = player1;
g.player2 = player2;
g.choice1 = choice1;
g.choice2 = choice2;
});
}
[[eosio::action]]
void reveal(uint64_t key) {
game_index games(_self, _self.value);
auto itr = games.find(key);
eosio_assert(itr != games.end(), "Game not found");
name p1 = itr->player1;
name p2 = itr->player2;
require_auth(p1);
require_auth(p2);
endgame(itr);
}
private:
struct [[eosio::table]] game {
uint64_t key;
name player1;
name player2;
std::string choice1;
std::string choice2;
uint64_t primary_key() const { return key; }
};
typedef eosio::multi_index<"games"_n, game> game_index;
void endgame(game_index::const_iterator itr) {
name winner;
std::string choice1 = itr->choice1;
std::string choice2 = itr->choice2;
if (choice1 == choice2) {
winner = "tie"_n;
} else if (choice1 == "rock" && choice2 == "scissors" || choice1 == "paper" && choice2 == "rock" || choice1 == "scissors" && choice2 == "paper") {
winner = itr->player1;
} else {
winner = itr->player2;
}
print("Winner: ", winner);
}
};
EOSIO_DISPATCH(rps, (play)(reveal))Full source code is here.
The contract allows players to play the game by specifying their choices of rock, paper, or scissors. The game is saved in a multi-index table, and the players can reveal the result by providing the game’s key. The contract includes two actions: play and reveal.
The play action is used to save the game with player1, player2, choice1, choice2.
The reveal action is used to reveal the game result, it requires the key of the game and the auth of player1 and player2.
The game struct is used to save the game details, it includes the primary key, player1, player2, choice1, and choice2.
The endgame function is used to reveal the game result and it takes a const reference to the game struct.