Layout in Memory

Solidity reserves four 32-byte slots in memory for special purposes in the EVM, and relies on a linear memory array that expands as data is written.

💡 NeoVM Difference

NeoVM does not have a linear byte-array memory model. Instead, memory in NeoVM is managed through an abstract evaluation stack consisting of structured StackItem objects (Integers, ByteArrays, Arrays, Maps).

Stack-Based Memory Allocation

When you declare a memory variable in Neo DevPack for Solidity, the compiler allocates a local slot on the execution stack.

function doSomething() public {
    // EVM: allocates memory starting at the free memory pointer
    // NeoVM: creates a new Array stack item and stores it in a local variable slot
    uint256[] memory myMemoryArray = new uint256[](5);
}

Structs in Memory

In memory, structs are represented as NeoVM Array types. The fields of the struct are accessed via their positional index within the array.

struct Proposal {
    address creator;
    uint256 votes;
}

// In memory: represented as a NeoVM Array `[creator, votes]`
Proposal memory p = Proposal(msg.sender, 0);

calldata vs memory

On Ethereum, calldata is a non-modifiable, non-persistent area where function arguments are stored, and behaves differently than memory.

On NeoVM, calldata is treated identically to memory. The compiler accepts the calldata keyword to maintain strict source compatibility with Ethereum contracts, but internally, function arguments are simply read from the execution stack.