Builtin types¶
| Rust | UDL | Kotlin |
|---|---|---|
bool |
boolean |
Boolean |
i8 / i16 / i32 / i64 |
i8 / i16 / i32 / i64 |
Byte / Short / Int / Long |
u8 / u16 / u32 / u64 |
u8 / u16 / u32 / u64 |
UByte / UShort / UInt / ULong |
f32 / f64 |
float / double |
Float / Double |
String |
string |
String |
Vec<u8> |
bytes |
ByteArray |
&[u8] (arguments only) |
[ByRef] bytes |
ByteArray |
std::time::SystemTime |
timestamp |
kotlin.time.Instant |
std::time::Duration |
duration |
kotlin.time.Duration |
Option<T> |
T? |
T? |
Vec<T> |
sequence<T> |
List<T> |
HashMap<K, V> |
record<K, V> |
Map<K, V> |
HashSet<T> |
— | Set<T> |
These types are copied when they cross the FFI. Unsigned integers map to Kotlin's unsigned types, so the full range is preserved.
Instant and Duration are the standard library types from kotlin.time. There is no dependency
on kotlinx-datetime. Generated files opt into kotlin.time.ExperimentalTime.
Borrowed bytes¶
A &[u8] argument lets Rust read a Kotlin ByteArray without copying it into a Rust-owned
buffer first:
#[uniffi::export]
pub fn sum_bytes(data: &[u8]) -> u64 {
data.iter().map(|b| *b as u64).sum()
}
sumBytes(byteArrayOf(1, 2, 3)) // 6u
The slice is only valid during the call, so Rust can't keep it. On Kotlin/Native the array is pinned for the duration of the call. On JVM and Android it is copied once into native memory.
Borrowed bytes work in functions, methods and constructors, but not in async functions, and not
as return values or callback arguments.