the following is an inheritance example from Solidity doc 0.83. My question is: can you deploy contract Named or contract PriceFeed on remix? I failed many times. I'm a beginner,I need your help. contract NameReg and contract Config are both abstract contracts, but contract Named can invoke their functions without inheritance declaration. why? Many thanks!
// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0 <0.9.0;
// This will report a warning due to deprecated selfdestruct
contract Owned {
constructor() { owner = payable(msg.sender); }
address payable owner;
}
// Use `is` to derive from another contract. Derived
// contracts can access all non-private members including
// internal functions and state variables. These cannot be
// accessed externally via `this`, though.
contract Destructible is Owned {
// The keyword `virtual` means that the function can change
// its behavior in derived classes ("overriding").
function destroy() virtual public {
if (msg.sender == owner) selfdestruct(owner);
}
}
// These abstract contracts are only provided to make the
// interface known to the compiler. Note the function
// without body. If a contract does not implement all
// functions it can only be used as an interface.
abstract contract Config {
function lookup(uint id) public virtual returns (address adr);
}
abstract contract NameReg {
function register(bytes32 name) public virtual;
function unregister() public virtual;
}
// Multiple inheritance is possible. Note that `Owned` is
// also a base class of `Destructible`, yet there is only a single
// instance of `Owned` (as for virtual inheritance in C++).
contract Named is Owned, Destructible {
constructor(bytes32 name) {
Config config = Config(0xD5f9D8D94886E70b06E474c3fB14Fd43E2f23970);
NameReg(config.lookup(1)).register(name);
}
// Functions can be overridden by another function with the same name and
// the same number/types of inputs. If the overriding function has different
// types of output parameters, that causes an error.
// Both local and message-based function calls take these overrides
// into account.
// If you want the function to override, you need to use the
// `override` keyword. You need to specify the `virtual` keyword again
// if you want this function to be overridden again.
function destroy() public virtual override {
if (msg.sender == owner) {
Config config = Config(0xD5f9D8D94886E70b06E474c3fB14Fd43E2f23970);
NameReg(config.lookup(1)).unregister();
// It is still possible to call a specific
// overridden function.
Destructible.destroy();
}
}
}
// If a constructor takes an argument, it needs to be
// provided in the header or modifier-invocation-style at
// the constructor of the derived contract (see below).
contract PriceFeed is Owned, Destructible, Named("GoldFeed") {
function updateInfo(uint newInfo) public {
if (msg.sender == owner) info = newInfo;
}
// Here, we only specify `override` and not `virtual`.
// This means that contracts deriving from `PriceFeed`
// cannot change the behavior of `destroy` anymore.
function destroy() public override(Destructible, Named) { Named.destroy(); }
function get() public view returns(uint r) { return info; }
uint info;
}