Why design patterns improve quality in Blockchain / Solidity - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a reusable contract template.

Blockchain / Solidity

contract [1] {
    // common functions here
}

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ATemplate

BMyContract

CMain

DToken

Attempts:

3 left

💡 Hint

Common Mistakes

Using specific contract names instead of a generic template.

Using a generic name like Template helps create reusable contract patterns.

2fill in blank

medium

Complete the code to implement a singleton pattern in a smart contract.

Blockchain / Solidity

contract Singleton {
    address private staticInstance;

    function getInstance() public view returns (address) {
        return [1];
    }
}

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Amsg.sender

BstaticInstance

Cowner

Daddress(this)

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the caller's address instead of the stored instance.

The singleton pattern returns the single stored instance address.

3fill in blank

hard

Fix the error in the code to properly use the factory pattern for contract creation.

Blockchain / Solidity

contract Factory {
    function create() public returns (address) {
        [1] newContract = new [1]();
        return address(newContract);
    }
}

contract Product {}

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AContract

BFactory

CInstance

DProduct

Attempts:

3 left

💡 Hint

Common Mistakes

Using the factory contract name as the new contract type.

The factory creates new Product contracts, so the type must be Product.

4fill in blank

hard

Fill both blanks to implement an observer pattern in Solidity.

Blockchain / Solidity

contract Subject {
    address[] public observers;

    function [1](address observer) public {
        observers.[2](observer);
    }
}

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AregisterObserver

Badd

Cpush

Dsubscribe

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect function or array method names.

The function to add observers is commonly named registerObserver, and push adds to the array.

5fill in blank

hard

Fill all three blanks to complete a decorator pattern example in Solidity.

Blockchain / Solidity

contract Base {
    function getValue() public pure virtual returns (uint) {
        return [1];
    }
}

contract Decorator is Base {
    Base base;
    constructor(Base _base) {
        base = _base;
    }
    function getValue() public view override returns (uint) {
        return base.getValue() [2] [3];
    }
}

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A10

B+

C5

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication instead of addition.

Returning wrong base value.

The base returns 10, and the decorator adds 5 using the plus operator.