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Developing Play-to-Earn Games in Solidity

Payment Processing

Understand how Solidity contracts process payments by exploring payable functions that accept ETH, the special receive and fallback functions that handle transfers without explicit calls, and best practices for securely sending ETH from contracts. This lesson enables you to manage deposits and withdrawals effectively while minimizing security risks like reentrancy.

We'll cover the following...

Sending money to a contract

Contracts have an address on the Ethereum network, just like EOAs; therefore, they can receive and send ETH.

Payable functions

A contract is able to receive ETH, for a specific purpose, by making the corresponding function payable using the payable keyword. ETH can then be sent as part of a call to that function.

For example, in the following contract, we define a deposit() function, allowing addresses (the msg.sender) to send ETH to the contract.

All ETH sent to a contract is held indistinctly in its total balance. So, a contract must include mechanisms to keep track of what belongs to which address.

In the below contract, the amount sent (msg.value) is added to the balance of the msg.sender, which we keep track of using the mapping defined in line 3.

Solidity
pragma solidity >=0.5.0 <0.9.0;
contract exampleDeposit {
    mapping(address => uint256) public balance;
    
    function deposit() public payable {
        balance[msg.sender] += msg.value;
    }
}

The receive function

On Ethereum, contract accounts have addresses that are indistinguishable from those ...