importing and using confusion

[TimeKeyRoll]

// SPDX-License-Identifier: GPL-3.0

pragma solidity >= 0.5.0 < 0.9.0;

import "./priceconvertor.sol";

contract Fund  {

    using priceconvertor for uint256;

Hi! If we have already this import "./priceconvertor.sol"; in the contract then why we are using using priceconvertor for uint256;.

can anyone please help me to understand this?

[shoaibshebi]

The directive using A for B, can be used to attach library functions of library A to a given type B. These functions will use the caller type as the type of their first parameter.

msg.value.getConversionRate

Here type of msg.value, which is uint256 is used implicitly for method getConversion() to tell it that: Hey function, the implicit parameter ethAmount that you are getting has the type of unit256.

So at top if you declare it as
using priceconvertor for uint
and later on used for uint256, it will through error.

👉 Here is the resource you can go through more. https://www.tutorialspoint.com/solidity/solidity_libraries.htm

Thanks

[bobanm]

Hello Master of Blockchain 🙂

It is not necessary to add using priceconvertor for uint256. Importing a file already makes compiler know the contents of the importet library. But adding using statement will allow you to make your code cleaner.

For example, if you're importing a function which adds 2 uint numbers:

function add(uint256 a, uint256 b) internal pure returns (uint256)

Without using, you would add 2 uints with:

sum = add(a, b);

With using, you can also get the same effect with syntax which is more OOP-style:

sum = a.add(b);

[TimeKeyRoll]

So it's just for the code to look good and clean. Right!?

[bobanm]

Yes, just some sugar coating for your code. Not mandatory at all.

[TimeKeyRoll]

Awesome. Thank you very much.

[bobanm]

I'm honored to be able to help the Master of Blockchain 😉

[TimeKeyRoll]

Thanks Mate. Name will make sense in a year too. Lol

[alymurtazamemon]

@MasterofBlockchain I would like to clarify the concept here about Libraries.

For using a library in our contract we need to use using LibraryName for <data-type> syntax.

data-type represents all of the returns types of functions for that you are using library (in our case it is uint256). If you have functions with different return types for example one function's return type is uint256 and another function's return type is a string and you want to use a library for both functions to access inside the contract then you specify two times using LibraryName for uint256 & using LibraryName for string.

And about the import statement so it is only required when your Library and contract are in separate files but if they both are in the same file you do not need that.

[TimeKeyRoll]

Or is there any case we can ignore these two keywords while using 'library' or there is a syntax that when we use 'library' and then we also have to use 'using' and 'for'.

And Beautifully explained and I have understood that. :)

[alymurtazamemon]

@MasterofBlockchain read here about library https://solidity-by-example.org/library/

[TimeKeyRoll]

OK ser.

[alymurtazamemon]

@MasterofBlockchain Please just Ali

[TimeKeyRoll]

Alright Ali. Thank you again.