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* Rename Base Camp to Base Learn * Rename Base Camp to Base Learn * Update learn link * change wallet type property from camel to snake case (#643) * Update api key requirement, minor style updates (#642) * Fix type and clarify inheritance ex (#655) * Document Reth snapshot URLs (#651) * feat(ecosystem): New additions to Ecosystem page (#647) * feat(ecosystem): New additions to Ecosystem page * chore(Ecosystem): Add image for Dynamic * Update preparing-for-fault-proofs-on-base-sepolia.md (#633) Update preparing-for-fault-proofs-on-base-sepolia * Fix conflict * fix conflict --------- Co-authored-by: Brendan from DeFi <brendan.forster@coinbase.com> Co-authored-by: Danyal Prout <danyal.prout@coinbase.com> Co-authored-by: wbnns <hello@wbnns.com> Co-authored-by: Olexandr Radovenchyk <radole1203@gmail.com>
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title, description, hide_table_of_contents
| title | description | hide_table_of_contents |
|---|---|---|
| Abstract Contracts | Learn how to make contracts that must be inherited by another contract. | false |
Abstract contracts can't exist on their own. Their functionality can only be utilized by a contract that inherits from them. In this lesson, you'll learn how to create an abstract contract.
Objectives
By the end of this lesson you should be able to:
- Use the virtual, override, and abstract keywords to create and use an abstract contract
Abstract Contracts
Continue with your Inheritance.sol file. Add ContractD as an abstract contract. Add a virtual function called whoAreYou function, but do not add any implementation for that function.
Reveal code
abstract contract ContractD {
function whoAreYou() public virtual view returns (string memory);
}
Inheriting from an Abstract Function
Update ContractA to inherit from ContractD.
You'll get a slightly confusing error that ContractA needs to be marked as abstract. Doing so is not the correct fix.
from solidity:
TypeError: Contract "ContractA" should be marked as abstract.
--> contracts/Inheritance.sol:25:1:
|
25 | contract ContractA is ContractB, ContractC, ContractD {
| ^ (Relevant source part starts here and spans across multiple lines).
Note: Missing implementation:
--> contracts/Inheritance.sol:6:5:
|
6 | function whoAreYou() public virtual view returns (string memory);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The clue for the correct solution is further down: Note: Missing implementation:
Only abstract contracts can declare functions that are not implemented. To fix this, provide an override implementation for whoAreYou in ContractA:
Reveal code
function whoAreYou() public override pure returns (string memory) {
return "I'm a person!";
}
Conclusion
In this lesson, you've learned how to implement and inherit from an abstract contract.