vortex-array 0.76.0

// SPDX-License-Identifier: Apache-2.0
// SPDX-FileCopyrightText: Copyright the Vortex contributors

//! Scalar function vtable machinery.
//!
//! This module contains the [`ScalarFnVTable`] trait and all built-in scalar function
//! implementations. Expressions ([`crate::expr::Expression`]) reference scalar functions
//! at each node.

use vortex_session::registry::Id;

use crate::scalar_fn::fns::byte_length::ByteLength;
use crate::scalar_fn::fns::ext_storage::ExtStorage;
use crate::scalar_fn::fns::get_item::GetItem;
use crate::scalar_fn::fns::literal::Literal;

mod vtable;
pub use vtable::*;

mod plugin;
pub use plugin::*;

mod foreign;
pub use foreign::*;

mod typed;
pub use typed::*;

mod erased;
pub use erased::*;

mod options;
pub use options::*;

mod signature;
pub use signature::*;

pub mod fns;
pub mod internal;
pub mod session;

/// A unique identifier for a scalar function.
pub type ScalarFnId = Id;

/// Private module to seal [`typed::DynScalarFn`].
mod sealed {
    use crate::scalar_fn::ScalarFnVTable;
    use crate::scalar_fn::typed::TypedScalarFnInstance;

    /// Marker trait to prevent external implementations of [`super::typed::DynScalarFn`].
    pub(crate) trait Sealed {}

    /// This can be the **only** implementor for [`super::typed::DynScalarFn`].
    impl<V: ScalarFnVTable> Sealed for TypedScalarFnInstance<V> {}
}

/// A scalar function has a negative cost if applying it to an array and
/// canonicalizing is cheaper than canonicalizing an array and applying it.
///
/// Example of negative cost expressions are byte_length(), ext_storage(), and get_item() since
/// they don't depend on input size.
///
/// Example of non-negative cost expression is like() as it's linear over
/// individual input.
pub fn is_negative_cost(id: ScalarFnId) -> bool {
    id == ScalarFnVTable::id(&ByteLength)
        || id == ScalarFnVTable::id(&ExtStorage)
        || id == ScalarFnVTable::id(&GetItem)
        || id == ScalarFnVTable::id(&Literal)
}