Dynamic Arrays

A dynamic-sized array in solidity can grow and shrink in size, the behavior is different when the array is in storage or memory.

The storage dynamic array does not need to declare the size at initialization since we can grow or shrink the array later.

contract StorageDynArray {
    uint[] public arr; // dynamic array in storage
}

The memory dynamic array act like a fixed sized array, we need to declare the size at initialization.

contract MemoryDynArray {
  function f() public {
    // dynamic array in memory with initial length 5
    uint[] memory arr = new uint[](5);
  }
}

Important

The push and pop methods are only available for dynamic arrays in storage, not in memory. Even though from the type signature of uint[] arr, it looks like a dynamic array, but compiler treats it as a fixed sized array in memory.

Getter

To reduce the gas cost, the getter function of array types only provide access to individual elements, not the whole array.

contract Alice {
    uint[] public arr;
}
 
contract Bob {
    function f() public view returns (uint) {
        Alice alice = new Alice();
        return alice.arr(0); // access the first element of the array
    }
}