An experiment to see how much do gas costs differ for the same action via different approaches

ExternalPureTest.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.4;

interface IUniSwapRouter02 {
    function WETH() external pure returns (address);
}

contract ExternalPureTest {
    address internal uniAddress = 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D;
    address public addr = 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D;
    
    // Set variable to an address given in place
    // Gas usage: 23475
    function getFromInline() external {
        addr = 0xc778417E063141139Fce010982780140Aa0cD5Ab;
    }
    
    // Set variable to an address from an external call
    // Gas usage: 26902
    function getFromExternal() external {
        addr = IUniSwapRouter02(0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D).WETH();
    }
    
    // Set variable to an address from an external call, whose address is read from a storage variable
    // Gas usage: 29101
    function getFromExternalWithStorageVar() external {
        addr = IUniSwapRouter02(uniAddress).WETH();
    }
}