Struct CastFunctionBuilder 

pub struct CastFunctionBuilder { /* private fields */ }

Builder for registering a custom DuckDB cast function.

A cast function converts values from a source type to a target type. Registering a cast lets DuckDB use it both for explicit CAST(x AS Target) syntax and (if an implicit cost is set) for automatic coercions.

Example

use quack_rs::cast::{CastFunctionBuilder, CastFunctionInfo, CastMode};
use quack_rs::types::TypeId;
use libduckdb_sys::{duckdb_function_info, duckdb_vector, idx_t};

unsafe extern "C" fn my_cast(
    _info: duckdb_function_info,
    _count: idx_t,
    _input: duckdb_vector,
    _output: duckdb_vector,
) -> bool {
    true // implement real conversion here
}

// fn register(con: libduckdb_sys::duckdb_connection)
//     -> Result<(), quack_rs::error::ExtensionError>
// {
//     unsafe {
//         CastFunctionBuilder::new(TypeId::Varchar, TypeId::Integer)
//             .function(my_cast)
//             .register(con)
//     }
// }

Implementations

impl CastFunctionBuilder

pub const fn new(source: TypeId, target: TypeId) -> Self

Creates a new builder that will cast source values into target values.

pub fn new_logical(source: LogicalType, target: LogicalType) -> Self

Creates a new builder using LogicalTypes for source and target.

Use this when the source or target types are complex (e.g. DECIMAL(18, 3), LIST(VARCHAR), etc.) and cannot be expressed as simple TypeId values.

pub const fn source(&self) -> Option<TypeId>

Returns the source type this cast converts from (if set via new).

Returns None if the source was set via new_logical.

Useful for introspection and for MockRegistrar.

pub const fn target(&self) -> Option<TypeId>

Returns the target type this cast converts to (if set via new).

Returns None if the target was set via new_logical.

Useful for introspection and for MockRegistrar.

pub fn function(self, f: CastFn) -> Self

Sets the cast callback.

pub const fn implicit_cost(self, cost: i64) -> Self

Sets the implicit cast cost.

When a non-negative cost is provided, DuckDB may use this cast automatically in expressions where an implicit coercion is needed. Lower cost means higher priority. A negative cost or omitting this method makes the cast explicit-only.

pub unsafe fn extra_info( self, ptr: *mut c_void, destroy: duckdb_delete_callback_t, ) -> Self

Attaches extra data to the cast function.

The pointer is available inside the callback via CastFunctionInfo::get_extra_info.

Safety

ptr must remain valid until DuckDB calls destroy, or for the lifetime of the database if destroy is None.

pub unsafe fn register( self, con: duckdb_connection, ) -> Result<(), ExtensionError>

Registers the cast function on the given connection.

Errors

Returns ExtensionError if:

• The function callback was not set.
• DuckDB reports a registration failure.

Safety

con must be a valid, open duckdb_connection.

Trait Implementations

impl Send for CastFunctionBuilder