I need help on this code

Question

I have few question:

1.

bool zeroForOne = params.tokenIn < params.tokenOut;

This code means: if params.tokenIn is less than params.tokenOut then make zeroForOne true, am i right?

2. There is a library named Path.sol in libraries directory, it has a function named numPools(). In a contract this library was imported and used forbytes, using Path for bytes, how this code is working then:

sqrtPriceX96AfterList = new uint160[](path.numPools());  

we are imported Path.sol but how path came in path.numPools()? Should not it be Path.numPools()?

3. A code is :

import "./libraries/Path.sol"
contract Check {
    using Path for bytes;
    struct SwapCallbackData {
        bytes path; // swap path
        address payer; // address who provides inout token in swaps
    }
    function _swap(
    uint256 amountIn,
    address recipient,
    uint160 sqrtPriceLimitX96,
    SwapCallbackData memory data
    ) internal returns (uint256 amountOut) {
    
    
    (address tokenIn, address tokenOut, uint24 tickSpacing) = data
    .path
    .decodeFirstPool();
  }
}

Here decodeFirstPool() is a function of Path.sol library, how data.path.decodeFirstPool() is working? I asked about the path in question 2, i am confused on how the connection was made between data and path??

Answer 1

Here are the answers:

1. Yes, you're correct bool zeroForOne would be true if params.tokenIn is greater than params.tokenOut.
2. as the path is of type bytes, when you call path.numPools() is actually calling the numPools() function from the Path library.
3. as data.path is of type bytes which is using Path library you can call the decodeFirstPool() function of Path Liberary.

P.S. using Path for bytes; creates a linkage between the Path library and the bytes data type.