Solidity: decode byte data into two structs - ethereum

Question

I have a function call which only accepts bytes data (dydx _getCallActions)
_getCallAction(bytes memory data)
During contract execution the data is passed to a user defined function named: "callFunction"
When decoding into a single struct, it works, however I want to to decode the data into two separate structs.
function callFunction(bytes calldata _data){
// This works, when passed in encoded data matching Struct1Type
Struct1Type memory data1 = abi.decode(_data, (Struct1Type));
}
function callFunction(bytes calldata _data){
// Doesnt work
Struct1Type memory data1, Struct2Type memory data2 = abi.decode(_data, (Struct1Type,Struct2Type));
}
I could decode the data into a single struct and then selectively cast it into the two desired structs, but this seems gas inefficient

Answer 1

You can split the array by the total byte length of the first struct rounded up to a multiplier of 32 - the slot length - and then decode each chunk separately.
In the example below, the length of Struct1Type is just 8 bytes, but the memory and storage slots take up the whole 32byte word. That's why we're splitting at the 32nd index.
Code:
pragma solidity ^0.8;
contract MyContract {
struct Struct1Type {
uint8 number;
}
struct Struct2Type {
uint16 number;
}
function callFunction(bytes calldata _data) external pure returns (Struct1Type memory, Struct2Type memory) {
// `:32` returns a chunk "from the beginning to the 32nd index"
Struct1Type memory data1 = abi.decode(_data[:32], (Struct1Type));
// `32:` returns a chunk "from the 32nd index to the end"
Struct2Type memory data2 = abi.decode(_data[32:], (Struct2Type));
return (data1, data2);
}
}
Input:
# two values: `1` and `2`
0x00000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000002
Output:
0: tuple(uint8): 1
1: tuple(uint16): 2