ink! F.A.Q.
This page will answer a number of common questions you may have when starting to build smart contracts for Substrate.
ink! F.A.Q.
What is the difference between memory and storage?
In ink! we refer memory to being the computer memory that is commonly known to programmers while with storage we refer to the contract instance's memory. The storage is backed up by the runtime in a data base. Accesses to it are considered to be slow.
Example
While a storage::Vec<T> stores every of its elements in a different cell in the contract storage, a storage::Value<memory::Vec<T>> would store all elements (and a length info) in a single cell. Smart contract writers can use this to optimize for certain use cases. Using a storage::Value<memory::Vec<T>> could probably be more efficient for a small amount of elements in the memory::Vec<T>. We advise to use the more general storage::Vec for storing information on the contract instance.
How do I run tests?
When building a smart contract with ink, you can define a set of tests.
For example, in the minimal flipper contract, you can find a small test at the bottom of the contract.
To run this test, type the following command:
cargo +nightly test
Contracts Module
How do I add the Contracts module to my custom chain?
You can follow our guide here for instructions to add the Contracts pallet and other FRAME pallets to your blockchain runtime.