Abstract contracts in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Abstract contracts

Define abstract contract

↓

Declare abstract functions

↓

Cannot deploy abstract contract

↓

Create derived contract

↓

Implement all abstract functions

↓

Deploy derived contract

↓

Use derived contract in blockchain

Abstract contracts define functions without code. They must be implemented in child contracts before deployment.

Execution Sample

Blockchain / Solidity

abstract contract Animal {
    function sound() public virtual returns (string memory);
}

contract Dog is Animal {
    function sound() public override returns (string memory) {
        return "Woof!";
    }
}

Defines an abstract contract Animal with an abstract function sound, then Dog implements sound.

Execution Table

Step	Action	Contract	Function	Result/State
1	Define abstract contract	Animal	sound()	Declared as abstract, no implementation
2	Try to deploy Animal	Animal	-	Error: Cannot deploy abstract contract
3	Define derived contract	Dog	-	Inherits Animal
4	Implement abstract function	Dog	sound()	Returns "Woof!"
5	Deploy Dog contract	Dog	-	Success: Contract deployed
6	Call sound() on Dog	Dog	sound()	Returns "Woof!"

💡 Deployment stops at abstract contract; only derived with full implementation can deploy.

Variable Tracker

Variable	Start	After Step 3	After Step 4	Final
Contract Animal	Abstract, no code	Abstract, no code	Abstract, no code	Abstract, no code
Contract Dog	Not defined	Defined, inherits Animal	sound() implemented	Deployed and usable
Function sound()	Abstract in Animal	Abstract in Animal	Implemented in Dog	Returns "Woof!"

Key Moments - 3 Insights

Why can't we deploy the abstract contract Animal directly?

Because Animal has an abstract function without implementation, deployment fails as shown in execution_table step 2.

What happens if Dog does not implement the abstract function sound()?

Dog would also be abstract and cannot be deployed, similar to Animal in step 2.

How do we know Dog's sound() function is used when called?

Because Dog overrides sound() with implementation, as shown in step 4 and calling it returns "Woof!" in step 6.

Visual Quiz - 3 Questions

Look at the execution_table, what happens at step 2 when trying to deploy Animal?

A Deployment succeeds with abstract functions

B Deployment fails because Animal is abstract

C Deployment succeeds but functions do nothing

D Deployment succeeds only if sound() is called

💡 Hint

Check execution_table row with Step 2 for deployment result

At which step does Dog implement the abstract function sound()?

A Step 1

B Step 3

C Step 4

D Step 5

💡 Hint

Look at execution_table row describing function implementation

If Dog did not implement sound(), what would happen when deploying Dog?

A Deployment would fail like Animal

B Deployment would succeed but sound() returns empty

C Deployment would succeed normally

D Deployment would succeed but Dog is abstract

💡 Hint

Refer to key_moments about implementation necessity and execution_table step 2

Concept Snapshot

abstract contract ContractName {
    function func() public virtual returns (type); // no body
}

contract Derived is ContractName {
    function func() public override returns (type) { ... } // must implement
}

- Abstract contracts cannot be deployed
- Derived contracts must implement all abstract functions
- Only fully implemented contracts can be deployed

Full Transcript

Abstract contracts in blockchain define functions without code, called abstract functions. These contracts cannot be deployed directly because they are incomplete. To use them, you create a derived contract that inherits the abstract contract and implements all its abstract functions. Only then can the derived contract be deployed and used on the blockchain. For example, an abstract contract Animal declares an abstract function sound(). The Dog contract inherits Animal and implements sound() to return "Woof!". Trying to deploy Animal fails, but deploying Dog succeeds. Calling sound() on Dog returns "Woof!". This ensures contracts have required functions implemented before deployment.