Collections

Using stype variables in arrays and maps

Shielded Arrays

Arrays of shielded types work like standard Solidity arrays. Keys (indices) must be non-shielded — using a shielded type as an array index is a compiler error.

They come in two forms:

• Dynamic (suint256[], sbool[], saddress[], etc.) — the length is stored as shielded.

• Fixed-size (suint256[5], sbool[4], saddress[3], etc.) — the length is a compile-time constant and publicly visible.

suint256[] private balances;     // dynamic — shielded length
sbool[4] private flags;          // fixed — length 4 is public

function example(uint256 i) public {
    balances[i] = suint256(100);   // valid — uint256 index
    flags[0] = sbool(true);        // valid — literal index
}

Even with dynamic shielded arrays, an upper bound on the length may be visible to observers monitoring gas costs, since gas usage scales with array operations.

Shielded Mappings

Mappings can have shielded values but keys cannot be shielded types. Using a shielded type as a mapping key is a compiler error. The standard mapping syntax applies.

mapping(address => suint256) private balances;    // valid
mapping(uint256 => sbool) private flags;          // valid
mapping(address => saddress) private recipients;  // valid

mapping(saddress => uint256) private lookup;      // INVALID — shielded key