Index expressions

^Syntax
IndexExpression :
   Expression [ Expression ]

Array and Map types can be indexed by by writing a square-bracket-enclosed expression after them. For arrays, the type of the index key has to be u256 whereas for Map types it has to be equal to the key type of the map.

Example:

contract Foo {

    balances: Map<address, u256>


    pub fn baz(mut self, mut values: Array<u256, 10>) {
        // Assign value at slot 5
        values[5] = 1000
        // Read value at slot 5
        let val1: u256 = values[5]

        // Assign value for address zero
        self.balances[address(0)] = 10000

        // Read balance of address zero
        let bal: u256 = self.balances[address(0)]
    }
}