Variables
In Solidity, there are 3 types of variables: local, state, and global. Local variables are not stored on the blockchain, while state variables are (and incur a much higher cost as a result). This is true of Arbitrum Stylus Rust smart contracts as well, although how they're defined is quite different.
In Rust, local variables are just ordinary variables you assign with let or let mut statements. Local variables are far cheaper than state variables, even on the EVM, however, Stylus local variables are more than 100x cheaper to allocate in memory than their Solidity equivalents.
Unlike Solidity, Rust was not built inherently with the blockchain in mind. It is a general purpose programming language. We therefore define specific storage types to explicitly denote values intended to be stored permanently as part of the contract's state. State variables cost the same to store as their Solidity equivalents.
Global variables in Solidity, such as msg.sender and block.timestamp, are available as function calls pulled in from the stylus_sdk with their Rust equivalents being vm().msg_sender() and vm().block_timestamp(), respectively. These variables provide information about the blockchain or the active transaction.
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Example
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