github.com/hasnat/dolt/go@v0.0.0-20210628190320-9eb5d843fbb7/libraries/doltcore/sqle/setalgebra/set.go (about)

     1  // Copyright 2020 Dolthub, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package setalgebra
    16  
    17  // Set is a well-defined collection of distint objects
    18  type Set interface {
    19  	// Union takes the current set and another set and returns a set containing all values from both.
    20  	Union(other Set) (Set, error)
    21  	// Interset takes the current set and another set and returns a set containing the values that are in both
    22  	Intersect(other Set) (Set, error)
    23  }
    24  
    25  // EmptySet is a Set implementation that has no values
    26  type EmptySet struct{}
    27  
    28  // Union takes the current set and another set and returns a set containing all values from both. When EmptySet is
    29  // unioned against any other set X, X will be the result.
    30  func (es EmptySet) Union(other Set) (Set, error) {
    31  	return other, nil
    32  }
    33  
    34  // Intersect takes the current set and another set and returns a set containing the values that are in both. When
    35  // EmptySet is intersected with any other set X, EmptySet will be returned.
    36  func (es EmptySet) Intersect(other Set) (Set, error) {
    37  	return es, nil
    38  }
    39  
    40  // UniversalSet is the set containing all values
    41  type UniversalSet struct{}
    42  
    43  // Union takes the current set and another set and returns a set containing all values from both. When
    44  // UniversalSet is unioned with any other set X, UniversalSet will be returned.
    45  func (us UniversalSet) Union(other Set) (Set, error) {
    46  	return us, nil
    47  }
    48  
    49  // Interset takes the current set and another set and returns a set containing the values that are in both. When
    50  // UniversalSet is intersected with any other set X, X will be the result.
    51  func (us UniversalSet) Intersect(other Set) (Set, error) {
    52  	return other, nil
    53  }