Known Limitations

Window functions are not available

DuckDB window functions (OVER (...) clauses) are implemented entirely in DuckDB's C++ layer and have no counterpart in the public C extension API.

This is not a gap in quack-rs or in libduckdb-sys — the relevant symbol (duckdb_create_window_function) simply does not exist in the C API:

Symbol	C API (1.4.x)?	C API (1.5.0+)?	C++ API?
`duckdb_create_window_function`	No	No	Yes
`duckdb_create_copy_function`	No	Yes	Yes
`duckdb_create_scalar_function`	Yes	Yes	Yes
`duckdb_create_aggregate_function`	Yes	Yes	Yes
`duckdb_create_table_function`	Yes	Yes	Yes
`duckdb_create_cast_function`	Yes	Yes	Yes

What this means for your extension:

If your extension needs window-function semantics, you can approximate them with aggregate functions in most cases (DuckDB will push down the window logic). True custom window operator registration requires writing a C++ extension.

If DuckDB exposes window registration in a future C API version, quack-rs will add wrappers in the corresponding release.

COPY functions (resolved in DuckDB 1.5.0)

DuckDB 1.5.0 added duckdb_create_copy_function and related symbols to the public C extension API. quack-rs wraps these in the copy_function module behind the duckdb-1-5 feature flag. See CopyFunctionBuilder for usage.

This was previously listed as a known limitation (no C API counterpart prior to 1.5.0).

Callback accessor wrappers (resolved)

quack-rs now wraps all major callback accessor functions — the C API functions used inside your callbacks to retrieve arguments, set errors, access bind data, etc.

Category	Wrapper type	Available
Scalar function execution	`ScalarFunctionInfo`	Always
Scalar function bind	`ScalarBindInfo`	`duckdb-1-5`
Scalar function init	`ScalarInitInfo`	`duckdb-1-5`
Aggregate function callbacks	`AggregateFunctionInfo`	Always
Table function bind	`BindInfo`	Always
Table function init	`InitInfo`	Always
Table function scan	`FunctionInfo`	Always
Cast function callbacks	`CastFunctionInfo`	Always
Copy function bind	`CopyBindInfo`	`duckdb-1-5`
Copy function global init	`CopyGlobalInitInfo`	`duckdb-1-5`
Copy function sink	`CopySinkInfo`	`duckdb-1-5`
Copy function finalize	`CopyFinalizeInfo`	`duckdb-1-5`

All callback accessor functions are now wrapped, including get_client_context on all callback types (returns a [ClientContext][crate::client_context::ClientContext]).

Complex type creation (resolved)

LogicalType now provides constructors for all complex parameterized types:

Method	Type created
`LogicalType::decimal(width, scale)`	`DECIMAL(p, s)`
`LogicalType::enum_type(members)`	`ENUM('a', 'b', ...)`
`LogicalType::array(child, size)`	`type[N]`
`LogicalType::union_type(members)`	`UNION(a INT, b VARCHAR)`
`LogicalType::list(child)`	`LIST(type)`
`LogicalType::struct_type(fields)`	`STRUCT(...)`
`LogicalType::map(key, value)`	`MAP(K, V)`

All constructors have _from_logical variants for nested complex types. Introspection methods (get_type_id, list_child_type, struct_child_count, decimal_width, etc.) are also available.

VARIANT and GEOMETRY types (resolved — exposed behind `duckdb-1-5-3`)

DuckDB v1.5.1 introduced the VARIANT type for Iceberg v3 support. As of DuckDB 1.5.3 it is present in the C type enum as DUCKDB_TYPE_VARIANT (41), and the GEOMETRY type (DUCKDB_TYPE_GEOMETRY, 40) is present as well.

quack-rs exposes these as TypeId::Variant and TypeId::Geometry, gated behind the duckdb-1-5-3 feature. That feature layers on top of duckdb-1-5 and requires libduckdb-sys >= 1.10503.1 (DuckDB 1.5.3). The separate gate exists because these type-enum values postdate the duckdb-1-5 feature's 1.5.0 floor (VARIANT only landed in 1.5.3); keeping them out of duckdb-1-5 preserves compatibility for consumers pinned to libduckdb-sys 1.5.0–1.5.2.

[dependencies]
quack-rs = { version = "0.13", features = ["duckdb-1-5-3"] }

Neither type yet has dedicated VectorReader/VectorWriter helpers; access their data via the raw pointer from duckdb_vector_get_data when needed.

quack-rs