Tuesday, August 29, 2017

Solidity Constant

Solidity supports to declare constant state variables and functions. A keyword constant is used to define constants in Solidity.

Constant State Variables

State variables can be declared as constant. All constant state variables should be assigned to a constant value at compile time. It can have an expression, but that expression should be evaluated to constant at compile time. Solidity only supports value types and string types as constants. Here is an example of defining constant static variable from Ethereum documentation. Currently in our contract we do not need this constant variables.

contract C {
    uint constant x = 32**22 + 8;
    string constant text = "abc";
    bytes32 constant myHash = keccak256("abc");

Constant Functions

Constant function are those functions which does not modify the state of the contract. These functions are used to return values from the contract. In our 0x service contract we defined a constant function which returns the address of the contractor.
/// @notice Get the contractor assigned to the service
/// @return contractor address
function getContractorAddress() public constant returns (address) {
    return contractor;

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