datafusion/expr/src/function.rs

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// to you under the Apache License, Version 2.0 (the
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//
//   http://www.apache.org/licenses/LICENSE-2.0
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//! Function module contains typing and signature for built-in and user defined functions.

use crate::ColumnarValue;
use crate::{Expr, PartitionEvaluator};
use arrow::datatypes::DataType;
use datafusion_common::Result;
use std::sync::Arc;

pub use datafusion_functions_aggregate_common::accumulator::{
    AccumulatorArgs, AccumulatorFactoryFunction, StateFieldsArgs,
};

pub use datafusion_functions_window_common::expr::ExpressionArgs;
pub use datafusion_functions_window_common::field::WindowUDFFieldArgs;
pub use datafusion_functions_window_common::partition::PartitionEvaluatorArgs;

#[derive(Debug, Clone, Copy)]
pub enum Hint {
    /// Indicates the argument needs to be padded if it is scalar
    Pad,
    /// Indicates the argument can be converted to an array of length 1
    AcceptsSingular,
}

/// Scalar function
///
/// The Fn param is the wrapped function but be aware that the function will
/// be passed with the slice / vec of columnar values (either scalar or array)
/// with the exception of zero param function, where a singular element vec
/// will be passed. In that case the single element is a null array to indicate
/// the batch's row count (so that the generative zero-argument function can know
/// the result array size).
pub type ScalarFunctionImplementation =
    Arc<dyn Fn(&[ColumnarValue]) -> Result<ColumnarValue> + Send + Sync>;

/// Factory that returns the functions's return type given the input argument types
pub type ReturnTypeFunction =
    Arc<dyn Fn(&[DataType]) -> Result<Arc<DataType>> + Send + Sync>;

/// Factory that creates a PartitionEvaluator for the given window
/// function
pub type PartitionEvaluatorFactory =
    Arc<dyn Fn() -> Result<Box<dyn PartitionEvaluator>> + Send + Sync>;

/// Factory that returns the types used by an aggregator to serialize
/// its state, given its return datatype.
pub type StateTypeFunction =
    Arc<dyn Fn(&DataType) -> Result<Arc<Vec<DataType>>> + Send + Sync>;

/// [crate::udaf::AggregateUDFImpl::simplify] simplifier closure
/// A closure with two arguments:
/// * 'aggregate_function': [crate::expr::AggregateFunction] for which simplified has been invoked
/// * 'info': [crate::simplify::SimplifyContext]
///
/// Closure returns simplified [Expr] or an error.
pub type AggregateFunctionSimplification = Box<
    dyn Fn(
        crate::expr::AggregateFunction,
        &crate::simplify::SimplifyContext,
    ) -> Result<Expr>,
>;

/// [crate::udwf::WindowUDFImpl::simplify] simplifier closure
/// A closure with two arguments:
/// * 'window_function': [crate::expr::WindowFunction] for which simplified has been invoked
/// * 'info': [crate::simplify::SimplifyContext]
///
/// Closure returns simplified [Expr] or an error.
pub type WindowFunctionSimplification = Box<
    dyn Fn(
        crate::expr::WindowFunction,
        &crate::simplify::SimplifyContext,
    ) -> Result<Expr>,
>;