《纸上谈兵·solidity》第 12 课：Solidity 函数选择器与 ABI 编码原理

selector = keccak256("函数名(参数类型列表)") 前 4 个字节

function transfer(address to, uint256 amount) public;

keccak256("transfer(address,uint256)") 
= 0xa9059cbb...
selector = 0xa9059cbb

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract SelectorExample {
    function getSelector() public pure returns (bytes4) {
        return this.transfer.selector;
    }

    function transfer(address to, uint256 amount) public pure returns (bool) {
        return true;
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract SelectorExample {
    function transfer(address to, uint256 amount) public pure returns (bool) {
        return true;
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "forge-std/Test.sol";
import "../src/SelectorExample.sol";

contract SelectorExampleTest is Test {
    SelectorExample example;

    function setUp() public {
        example = new SelectorExample();
    }

    function testSelector() public {
        bytes4 selector = example.transfer.selector;
        assertEq(selector, bytes4(keccak256("transfer(address,uint256)")));
    }

    function testABIEncoding() public {
        address to = address(0x123);
        uint256 amount = 100;

        bytes memory encoded = abi.encodeWithSelector(
            example.transfer.selector,
            to,
            amount
        );

        emit log_bytes(encoded);
    }
}

➜  counter git:(main) ✗ forge test --match-path test/SelectorExample.t.sol -vvv
[⠊] Compiling...
[⠆] Compiling 1 files with Solc 0.8.29
[⠰] Solc 0.8.29 finished in 1.26s
Compiler run successful with warnings:
Warning (5667): Unused function parameter. Remove or comment out the variable name to silence this warning.
 --> src/SelectorExample.sol:5:23:
  |
5 |     function transfer(address to, uint256 amount) public pure returns (bool) {
  |                       ^^^^^^^^^^

Warning (5667): Unused function parameter. Remove or comment out the variable name to silence this warning.
 --> src/SelectorExample.sol:5:35:
  |
5 |     function transfer(address to, uint256 amount) public pure returns (bool) {
  |                                   ^^^^^^^^^^^^^^


Ran 2 tests for test/SelectorExample.t.sol:SelectorExampleTest
[PASS] testABIEncoding() (gas: 5278)
Logs:
  0xa9059cbb00000000000000000000000000000000000000000000000000000000000001230000000000000000000000000000000000000000000000000000000000000064

[PASS] testSelector() (gas: 5512)
Suite result: ok. 2 passed; 0 failed; 0 skipped; finished in 8.14ms (2.12ms CPU time)

Ran 1 test suite in 438.24ms (8.14ms CPU time): 2 tests passed, 0 failed, 0 skipped (2 total tests)

(bool success, bytes memory data) = target.call(
    abi.encodeWithSelector(
        bytes4(keccak256("transfer(address,uint256)")),
        to,
        amount
    )
);