- Smart contracts communicate with each other in the form of actions and shared memory database access.
- A contract can read the state of another contract's database as long as it is included within the read scope of the transactions with an async vibe.
- This can be achieved by using one of two communication modes - inline and deferred. One can think of em' as sync and async.
Inline - Inline is a guaranteed to execute with current transaction or unwind; no notification will be communicated regardless of success or failure. Inline operates with the same scopes and authorities the original transaction had.
Deferred - Defer will get scheduled later at producer's discretion; it's possible to communicate the result of of the communication or can simply timeout. Deferred can reach out to different scopes and carry the authority of the contract taht sends em.
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We've put actions and constructors in public scope.
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Each action represents a single operation inside the smart contract.
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[[eosio::action]]is the indication to eosiocpp compiler. -
Each action operates within its own environment know as action context.
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Context provides :
- working memory: Here action maintains working state.
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Before processing an action EOSIO sets up a clean working memory for the action.
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The only way to pass state among action is to persist it to and retrive it from the EOSIO databse
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This can be achieved with multi-index. It allows us to read/modify persistent state in the EOSIO database.
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One can define a table object with primary key. (take a look at Players.cpp)
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Once the object is ready, we need to typedef our multi-index as follows:
typedef multi_index<"table_name"_n, object_template_to_use> multi_index_name;