1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

use crate::Array;

/// A possibly [`Scalar`] [`Array`]
///
/// This allows optimised binary kernels where one or more arguments are constant
///
/// ```
/// # use arrow_array::*;
/// # use arrow_buffer::{BooleanBuffer, MutableBuffer, NullBuffer};
/// # use arrow_schema::ArrowError;
/// #
/// fn eq_impl<T: ArrowPrimitiveType>(
///     a: &PrimitiveArray<T>,
///     a_scalar: bool,
///     b: &PrimitiveArray<T>,
///     b_scalar: bool,
/// ) -> BooleanArray {
///     let (array, scalar) = match (a_scalar, b_scalar) {
///         (true, true) | (false, false) => {
///             let len = a.len().min(b.len());
///             let nulls = NullBuffer::union(a.nulls(), b.nulls());
///             let buffer = BooleanBuffer::collect_bool(len, |idx| a.value(idx) == b.value(idx));
///             return BooleanArray::new(buffer, nulls);
///         }
///         (true, false) => (b, (a.null_count() == 0).then(|| a.value(0))),
///         (false, true) => (a, (b.null_count() == 0).then(|| b.value(0))),
///     };
///     match scalar {
///         Some(v) => {
///             let len = array.len();
///             let nulls = array.nulls().cloned();
///             let buffer = BooleanBuffer::collect_bool(len, |idx| array.value(idx) == v);
///             BooleanArray::new(buffer, nulls)
///         }
///         None => BooleanArray::new_null(array.len()),
///     }
/// }
///
/// pub fn eq(l: &dyn Datum, r: &dyn Datum) -> Result<BooleanArray, ArrowError> {
///     let (l_array, l_scalar) = l.get();
///     let (r_array, r_scalar) = r.get();
///     downcast_primitive_array!(
///         (l_array, r_array) => Ok(eq_impl(l_array, l_scalar, r_array, r_scalar)),
///         (a, b) => Err(ArrowError::NotYetImplemented(format!("{a} == {b}"))),
///     )
/// }
///
/// // Comparison of two arrays
/// let a = Int32Array::from(vec![1, 2, 3, 4, 5]);
/// let b = Int32Array::from(vec![1, 2, 4, 7, 3]);
/// let r = eq(&a, &b).unwrap();
/// let values: Vec<_> = r.values().iter().collect();
/// assert_eq!(values, &[true, true, false, false, false]);
///
/// // Comparison of an array and a scalar
/// let a = Int32Array::from(vec![1, 2, 3, 4, 5]);
/// let b = Int32Array::new_scalar(1);
/// let r = eq(&a, &b).unwrap();
/// let values: Vec<_> = r.values().iter().collect();
/// assert_eq!(values, &[true, false, false, false, false]);
pub trait Datum {
    /// Returns the value for this [`Datum`] and a boolean indicating if the value is scalar
    fn get(&self) -> (&dyn Array, bool);
}

impl<T: Array> Datum for T {
    fn get(&self) -> (&dyn Array, bool) {
        (self, false)
    }
}

impl Datum for dyn Array {
    fn get(&self) -> (&dyn Array, bool) {
        (self, false)
    }
}

impl Datum for &dyn Array {
    fn get(&self) -> (&dyn Array, bool) {
        (*self, false)
    }
}

/// A wrapper around a single value [`Array`] that implements
/// [`Datum`] and indicates [compute] kernels should treat this array
/// as a scalar value (a single value).
///
/// Using a [`Scalar`] is often much more efficient than creating an
/// [`Array`] with the same (repeated) value.
///
/// See [`Datum`] for more information.
///
/// # Example
///
/// ```rust
/// # use arrow_array::{Scalar, Int32Array, ArrayRef};
/// # fn get_array() -> ArrayRef { std::sync::Arc::new(Int32Array::from(vec![42])) }
/// // Create a (typed) scalar for Int32Array for the value 42
/// let scalar = Scalar::new(Int32Array::from(vec![42]));
///
/// // Create a scalar using PrimtiveArray::scalar
/// let scalar = Int32Array::new_scalar(42);
///
/// // create a scalar from an ArrayRef (for dynamic typed Arrays)
/// let array: ArrayRef = get_array();
/// let scalar = Scalar::new(array);
/// ```
///
/// [compute]: https://docs.rs/arrow/latest/arrow/compute/index.html
#[derive(Debug, Copy, Clone)]
pub struct Scalar<T: Array>(T);

impl<T: Array> Scalar<T> {
    /// Create a new [`Scalar`] from an [`Array`]
    ///
    /// # Panics
    ///
    /// Panics if `array.len() != 1`
    pub fn new(array: T) -> Self {
        assert_eq!(array.len(), 1);
        Self(array)
    }

    /// Returns the inner array
    #[inline]
    pub fn into_inner(self) -> T {
        self.0
    }
}

impl<T: Array> Datum for Scalar<T> {
    fn get(&self) -> (&dyn Array, bool) {
        (&self.0, true)
    }
}