The withdraw pattern in Solidity

Pull, don't push: zero the balance before sending.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

// Pull, don't push: zero the balance before sending anything.
contract StallPayouts {
    mapping(address => uint256) public owed;

    function credit(address vendor) external payable {
        owed[vendor] += msg.value;
    }

    function withdraw() external {
        uint256 amount = owed[msg.sender];
        require(amount > 0, "nothing owed");
        owed[msg.sender] = 0;  // effects before interaction
        (bool ok, ) = msg.sender.call{value: amount}("");
        require(ok, "send failed");
    }
}

How it works

1. Credits accumulate in owed; nobody is paid unasked.
2. The balance zeroes before the send — effects first.
3. call{value: amount}("") sends; the bool is checked.

Keywords and builtins used here

• address
• bool
• contract
• external
• function
• mapping
• payable
• public
• require
• uint256

The run, in numbers

Lines

19

Characters to type

505

Tokens

95

Three-star pace

55 tpm

At the three-star pace of 55 tokens a minute, this run takes about 104 seconds.

Type this snippet

Step 3 of 3 in Ether & events, step 13 of 28 in Language basics.

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