Some items in solidity like the type address has a couple of built in function for transferring ether or querying balance. The functions are the followings:
<address>.balance (uint256):
balance of the Address in Wei
<address>.transfer(uint256 amount):
send given amount of Wei to Address, throws on failure
<address>.send(uint256 amount) returns (bool):
send given amount of Wei to Address, returns false on failure
you can not make inheritance from a built in type, however what you can do is to define the same functions in a custom class, indirectly overwriting these functions.
contract ExtAddress{
function balance (uint256){
}
function transfer(uint256 amount){
}
function send(uint256 amount) returns (bool){
}
}
They do not directly overwrite the address functions, however in certain situations the functions can be exchanged for the first site.
