3.2. Elementary Types#

Syntax#

ElementaryType = (* variant: *) BOOL_KEYWORD
               | (* variant: *) BYTE_KEYWORD (* Deprecated in 0.8.0 *)
               | (* variant: *) STRING_KEYWORD
               | (* variant: *) AddressType
               | (* variant: *) BYTES_KEYWORD
               | (* variant: *) INT_KEYWORD
               | (* variant: *) UINT_KEYWORD
               | (* variant: *) FIXED_KEYWORD
               | (* variant: *) UFIXED_KEYWORD;

AddressType = (* address_keyword: *) ADDRESS_KEYWORD
              (* payable_keyword: *) PAYABLE_KEYWORD?;

Address Types#

The address type comes in two flavours, which are largely identical:

• address: Holds a 20 byte value (size of an Ethereum address).
• address payable: Same as address, but with the additional members transfer and send.

Hexadecimal literals that pass the address checksum test, for example 0xdCad3a6d3569DF655070DEd06cb7A1b2Ccd1D3AF are of address type. Hexadecimal literals that are between 39 and 41 digits long and do not pass the checksum test produce an error. You can prepend (for int types) or append (for bytesNN types) zeros to remove the error.

Fixed-Size Byte Arrays#

The value types bytes1, bytes2, bytes3, …, bytes32 hold a sequence of bytes from one to up to 32.

Dynamic String and Byte Arrays#

The bytes type is similar to bytes1[], but it is packed tightly in calldata and memory.

Variables of type string are equal to bytes but do not allow length or index access. If you want to access the byte-representation of a string s, use bytes(s). Keep in mind that you are accessing the low-level bytes of the UTF-8 representation, and not the individual characters.

Memory arrays with dynamic length can be created using the new keyword:

contract MyContract {
    function myFunction(uint length) public pure {
        bytes memory b = new bytes(length);
    }
}