What is the difference between a method call and the use of SEND_INLINE_ACTION?

Question

in looking at the code for eosio.token (https://github.com/EOSIO/eos/blob/master/contracts/eosio.token/eosio.token.cpp) the issue method calls the transfer method at the bottom, but instead of just calling it (e.g. token::transfer(...)) it uses the SEND_INLINE_ACTION macro (or whatever that is)

why?

p.s. I've looked at the docs for that function (https://developers.eos.io/eosio-cpp/reference#send_inline_action) but the description merely states that the function "Send inline action", as if I couldn't read that from the name of the function. there really isn't any point in having documentation like that. can anyone explain what an "inline" action is? and what is being sent? an action can be called, but sent?

Answer 1

You can call any function of a smart contract from within the smart contract, however only functions labelled as actions can be called from outside of the smart contract.

So if you have a function in contract A that needs to call a function from contract B, you would have to do this by sending an action.

An inline action means that the action has to be performed as part of the current transaction, meaning if the inline action failed, then so would your entire transaction, which is often the desired behaviour.

Answer 2

You can send an inline action without SEND_INLINE_ACTION macro, but it checks the type of action before sending it. (A little bit safer because SEND_INLINE_ACTION with invalid action type produces an error during compilation)