How can i burn the tokens i create with eosio.token

Question

I want to burn the tokens i created for some reasons, I found the method "retire" in eosio.token. But, this method only change the supply of the token, the maximum supply is still the same as it is originally.

 {   "rows": [{
       "supply": "9000000000.0000 SYS",
       "max_supply": "**10000000000.0000** SYS",
       "issuer": "eosio"
     }   ],   "more": false 
 }

So, Is there any other method for that ?

Answer 1

The default implementation of eosio.token doesn't support burn you describe. Add next code block to your token contract.

void token::burn( const asset& quantity, const string& memo ) {
   auto sym = quantity.symbol;
   check( sym.is_valid(), "invalid symbol name" );
   check( memo.size() <= 256, "memo has more than 256 bytes" );

   stats statstable( get_self(), sym.code().raw() );
   auto existing = statstable.find( sym.code().raw() );
   check( existing != statstable.end(), "token with symbol does not exist" );
   const auto& st = *existing;

   require_auth( st.issuer );
   check( quantity.is_valid(), "invalid quantity" );
   check( quantity.amount > 0, "must burn positive quantity" );

   check( quantity.symbol == st.supply.symbol, "symbol precision mismatch" );

   statstable.modify( st, same_payer, [&]( auto& s ) {
      s.supply -= quantity;
      s.max_supply -= quantity; // this line is added compared to `token::retire`
   });

   sub_balance( st.issuer, quantity );
}