CODEWITHSUNDEEP
c++attributes
mschoenebeck
mschoenebeck

Reputation: 407

C++ language feature: double square brackets [[ ]] used in class or method declaration

I am currently diving into smart contract development for eosio. By walking through the tutorials I noticed a certain C++ language feature I have never seen before:

#include <eosio/eosio.hpp>

using namespace eosio;

class [[eosio::contract]] hello : public contract {
  public:
      using contract::contract;

      [[eosio::action]]
      void hi( name user ) {
         print( "Hello, ", user);
      }
};

My question is what does the [[eosio::contract]] in the class declaration and the [[eosio::action]] in the method declaration mean? What is the term for this C++ language feature?

Upvotes: 1

Views: 826

Answers (1)

eerorika
eerorika

Reputation: 238311

What is the term for this C++ language feature?

The double square brackets are syntax for attributes. They are specified in the C++ standard section [dcl.attr]:

[dcl.attr]

Attributes specify additional information for various source constructs such as types, variables, names, blocks, or translation units.

My question is what does the [[eosio::contract]] in the class declaration and the [[eosio::action]] in the method declaration mean?

eosio is a non-standard attribute-namespace, so you should consult their documentation for the meaning of their custom attributes.

Upvotes: 2

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