Mastering Blockchain Programming with Solidity

Carefully making external function calls

The Solidity smart contracts do have a size limit for deployment. A contract that consumes less than 8 million gas at the time of deployment can be deployed on the Ethereum blockchain at the moment. In the future, this limit of 8 million gas could be increased. When your contracts are big enough and cannot be deployed in a single block, they need to be further divided into multiple small contracts. You can break a big contract into multiple small contracts and libraries and interconnect these contracts via function calls with the required authorization.

Not only that, if your contracts needed to communicate with some external service, you would need to make external function calls to external contracts. ...