> Aztec.nr API reference, v6.0.0 (mainnet and testnet). Index: https://docs.aztec.network/aztec-nr-api/v6.0.0/llms.txt

# Type alias TransientArray

Module: `noir_aztec::transient`

```rust
pub type TransientArray<T> = UnconstrainedArray<T, TransientOracles>;
```

A dynamically sized array that lives for the duration of a single top-level PXE call.

Like [`EphemeralArray`](/aztec-nr-api/v6.0.0/noir_aztec/ephemeral/type.EphemeralArray.md), transient arrays are backed by in-memory storage on the PXE side rather than a persistent database, and each logical operation is a single oracle call. The difference is lifetime and visibility: a `TransientArray` is shared across **all call frames of the same contract (private and utility alike)** within one top-level PXE call (transaction simulation or utility call), whereas an `EphemeralArray` is confined to a single call frame.

In order of increasing lifetime: an [`EphemeralArray`](/aztec-nr-api/v6.0.0/noir_aztec/ephemeral/type.EphemeralArray.md) lives for one call frame, a `TransientArray` for one top-level PXE call, and a [`CapsuleArray`](/aztec-nr-api/v6.0.0/noir_aztec/capsules/struct.CapsuleArray.md) is persistent.

## Privacy / Isolation

Arrays are keyed by `(executing contract address, slot)`. The contract address is supplied by PXE from the executing context, so a contract can only ever access its own transient arrays; other contracts called within the same top-level PXE call cannot see them, and this isolation holds across the private/utility boundary.

**Note on re-entrancy:** because visibility is flat within a contract, if the same contract is entered more than once in a top-level PXE call (e.g. it calls back into itself, or a private frame calls one of its own functions), those frames share the same arrays at the same slots. This differs from `EphemeralArray`, where even two frames of the same contract are isolated.

## Use Cases

Use this to pass not-to-be-persisted data between a contract's own frames (private or utility) within one top-level PXE call. For data confined to a single call frame, prefer [`EphemeralArray`](/aztec-nr-api/v6.0.0/noir_aztec/ephemeral/type.EphemeralArray.md). For data that must persist indefinitely, use [`CapsuleArray`](/aztec-nr-api/v6.0.0/noir_aztec/capsules/struct.CapsuleArray.md).