Solidity Basics II

Predefined global variables

A small number of global objects are accessible to a contract during execution in the EVM. These objects are msg, block, and tx. The values of these objects are read-only and cannot be modified within the smart contract.

The msg object

The msg object contains several fields that provide information about the current transaction call. Here’s a list of the most commonly used fields:

• msg.sender: The address that initiated the contract call (If the contract is called directly by an EOA transaction, then this is the address of the EOA account, but otherwise, it’s a contract address).

• msg.value: The value (in Wei) of Ether sent with the transaction.

• msg.data: The data payload for calls to a CA.

• msg.sig: It’s the function selector.

The block object

The block object contains several fields that provide information about the current block. Here’s a list of the most commonly used fields:

• block.number: The number of the current block.

• block.timestamp: The timestamp of the current block, calculated in seconds since the Unix epoch.

• block.gaslimit: The maximum amount of gas the current block can contain.

• block.coinbase: The address of the miner that mined the current block.

The tx object

The tx object contains transaction related information:

• tx.gasprice: The gas price specified by the sender of the transaction.

• tx.origin: The original sender of the transaction.

Functions

In Solidity, functions are used to perform specific tasks or operations within a smart contract. Functions can be defined with specific input parameters and may return a value. The syntax to declare a function in Solidity is as follows: