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
153

// Copyright 2018 Mozilla
//
// Licensed 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 core_traits::{
    Binding,
    TypedValue,
};

/// The result you get from a 'rel' query, like:
///
/// ```edn
/// [:find ?person ?name
///  :where [?person :person/name ?name]]
/// ```
///
/// There are three ways to get data out of a `RelResult`:
/// - By iterating over rows as slices. Use `result.rows()`. This is efficient and is
///   recommended in two cases:
///   1. If you don't need to take ownership of the resulting values (e.g., you're comparing
///      or making a modified clone).
///   2. When the data you're retrieving is cheap to clone. All scalar values are relatively
///      cheap: they're either small values or `Rc`.
/// - By direct reference to a row by index, using `result.row(i)`. This also returns
///   a reference.
/// - By consuming the results using `into_iter`. This allocates short-lived vectors,
///   but gives you ownership of the enclosed `TypedValue`s.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct RelResult<T> {
    pub width: usize,
    pub values: Vec<T>,
}

pub type StructuredRelResult = RelResult<Binding>;

impl<T> RelResult<T> {
    pub fn empty(width: usize) -> RelResult<T> {
        RelResult {
            width: width,
            values: Vec::new(),
        }
    }

    pub fn is_empty(&self) -> bool {
        self.values.is_empty()
    }

    pub fn row_count(&self) -> usize {
        self.values.len() / self.width
    }

    pub fn rows(&self) -> ::std::slice::Chunks<T> {
        // TODO: Nightly-only API `exact_chunks`. #47115.
        self.values.chunks(self.width)
    }

    pub fn row(&self, index: usize) -> Option<&[T]> {
        let end = self.width * (index + 1);
        if end > self.values.len() {
            None
        } else {
            let start = self.width * index;
            Some(&self.values[start..end])
        }
    }
}

#[test]
fn test_rel_result() {
    let empty = StructuredRelResult::empty(3);
    let unit = StructuredRelResult {
        width: 1,
        values: vec![TypedValue::Long(5).into()],
    };
    let two_by_two = StructuredRelResult {
        width: 2,
        values: vec![TypedValue::Long(5).into(), TypedValue::Boolean(true).into(),
                     TypedValue::Long(-2).into(), TypedValue::Boolean(false).into()],
    };

    assert!(empty.is_empty());
    assert!(!unit.is_empty());
    assert!(!two_by_two.is_empty());

    assert_eq!(empty.row_count(), 0);
    assert_eq!(unit.row_count(), 1);
    assert_eq!(two_by_two.row_count(), 2);

    assert_eq!(empty.row(0), None);
    assert_eq!(unit.row(1), None);
    assert_eq!(two_by_two.row(2), None);

    assert_eq!(unit.row(0), Some(vec![TypedValue::Long(5).into()].as_slice()));
    assert_eq!(two_by_two.row(0), Some(vec![TypedValue::Long(5).into(), TypedValue::Boolean(true).into()].as_slice()));
    assert_eq!(two_by_two.row(1), Some(vec![TypedValue::Long(-2).into(), TypedValue::Boolean(false).into()].as_slice()));

    let mut rr = two_by_two.rows();
    assert_eq!(rr.next(), Some(vec![TypedValue::Long(5).into(), TypedValue::Boolean(true).into()].as_slice()));
    assert_eq!(rr.next(), Some(vec![TypedValue::Long(-2).into(), TypedValue::Boolean(false).into()].as_slice()));
    assert_eq!(rr.next(), None);
}

// Primarily for testing.
impl From<Vec<Vec<TypedValue>>> for RelResult<Binding> {
    fn from(src: Vec<Vec<TypedValue>>) -> Self {
        if src.is_empty() {
            RelResult::empty(0)
        } else {
            let width = src.get(0).map(|r| r.len()).unwrap_or(0);
            RelResult {
                width: width,
                values: src.into_iter().flat_map(|r| r.into_iter().map(|v| v.into())).collect(),
            }
        }
    }
}

pub struct SubvecIntoIterator<T> {
    width: usize,
    values: ::std::vec::IntoIter<T>,
}

impl<T> Iterator for SubvecIntoIterator<T> {
    // TODO: this is a good opportunity to use `SmallVec` instead: most queries
    // return a handful of columns.
    type Item = Vec<T>;
    fn next(&mut self) -> Option<Self::Item> {
        let result: Vec<_> = (&mut self.values).take(self.width).collect();
        if result.is_empty() {
            None
        } else {
            Some(result)
        }
    }
}

impl<T> IntoIterator for RelResult<T> {
    type Item = Vec<T>;
    type IntoIter = SubvecIntoIterator<T>;

    fn into_iter(self) -> Self::IntoIter {
        SubvecIntoIterator {
            width: self.width,
            values: self.values.into_iter(),
        }
    }
}