Foundry Book

Struct Encoding

Structs are user defined types that can group several variables:

struct MyStruct {
    address addr;
    uint256 amount;
}

Only the new ABI coder v2 can encode and decode arbitrarily nested arrays and structs. Since Solidity 0.8.0 it is activated by default, prior to that it needs to be activated via pragma experimental ABIEncoderV2.

Solidity structs map to the ABI type "tuple". For more information on how Solidity types map to ABI types see Mapping Solidity to ABI types in the Solidity documentation.

Structs are therefore encoded and decoded as tuples. So the struct we defined above, MyStruct, maps to the tuple (address,uint256) in terms of the ABI.

Let's see how this works in a contract:

pragma solidity =0.8.15;


contract Test {
    struct MyStruct {
        address addr;
        uint256 amount;
    }
    function f(MyStruct memory t) public pure {}
}

The ABI of the f function in this contract is:

{
	"inputs": [
		{
			"components": [
				{
					"internalType": "address",
					"name": "addr",
					"type": "address"
				},
				{
					"internalType": "uint256",
					"name": "amount",
					"type": "uint256"
				}
			],
			"internalType": "struct Test.MyStruct",
			"name": "t",
			"type": "tuple"
		}
	],
	"name": "f",
	"outputs": [],
	"stateMutability": "pure",
	"type": "function"
}

which reads: The function f takes 1 input of type tuple with two components of type address and uint256.