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vector.go
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vector.go
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// Copyright 2018 the u-root Authors. All rights reserved
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package vector implements persistent vector.
package vector
// Vectors from elvish. I'm not convinced a lot of the claims were correct
// so I stripped the comment. I'm not sure how much of what this does we need,
// e.g. SubVector, but we'll see.
type Vector interface {
// Len returns the length of the vector.
Len() int
// Index returns the i-th element of the vector, if it exists. The second
// return value indicates whether the element exists.
Index(i int) (interface{}, bool)
// Assoc returns an almost identical Vector, with the i-th element
// replaced. If the index is smaller than 0 or greater than the length of
// the vector, it returns nil. If the index is equal to the size of the
// vector, it is equivalent to Cons.
Assoc(i int, val interface{}) Vector
// Cons returns an almost identical Vector, with an additional element
// appended to the end.
Cons(val interface{}) Vector
// Pop returns an almost identical Vector, with the last element removed. It
// returns nil if the vector is already empty.
Pop() Vector
// SubVector returns a subvector containing the elements from i up to but
// not including j.
SubVector(i, j int) Vector
// Iterator returns an iterator over the vector.
Iterator() Iterator
}
// Iterator is an iterator over vector elements. It can be used like this:
//
// for it := v.Iterator(); it.HasElem(); it.Next() {
// elem := it.Elem()
// // do something with elem...
// }
type Iterator interface {
// Elem returns the element at the current position.
Elem() interface{}
// HasElem returns whether the iterator is pointing to an element.
HasElem() bool
// Next moves the iterator to the next position.
Next()
}
type vector struct {
pos int
nodes []interface{}
}
// Empty is an empty Vector.
var Empty Vector = &vector{}
// Count returns the number of elements in a Vector.
func (v *vector) Len() int {
return len(v.nodes)
}
func (v *vector) Index(i int) (interface{}, bool) {
if i < 0 || i >= len(v.nodes) {
return nil, false
}
return v.nodes[i], true
}
func (v *vector) Assoc(i int, val interface{}) Vector {
if i < 0 || i > len(v.nodes) {
return nil
}
n := append(append(v.nodes[:i], val), v.nodes[i:]...)
return &vector{nodes: n}
}
func (v *vector) Cons(val interface{}) Vector {
return &vector{nodes: append(v.nodes, val)}
}
func (v *vector) Pop() Vector {
switch len(v.nodes) {
case 0:
return nil
case 1:
return Empty
}
return &vector{nodes: v.nodes[:len(v.nodes)-1]}
}
func (v *vector) SubVector(begin, end int) Vector {
if begin < 0 || begin > end || end > len(v.nodes) {
return nil
}
return &subVector{v, begin, end}
}
func (v *vector) Iterator() Iterator {
return newIterator(v)
}
type subVector struct {
v *vector
begin int
end int
}
func (s *subVector) Len() int {
return s.end - s.begin
}
func (s *subVector) Index(i int) (interface{}, bool) {
if i < 0 || s.begin+i >= s.end {
return nil, false
}
return s.v.Index(s.begin + i)
}
func (s *subVector) Assoc(i int, val interface{}) Vector {
if i < 0 || s.begin+i > s.end {
return nil
} else if s.begin+i == s.end {
return s.Cons(val)
}
return s.v.Assoc(s.begin+i, val).SubVector(s.begin, s.end)
}
func (s *subVector) Cons(val interface{}) Vector {
return s.v.Assoc(s.end, val).SubVector(s.begin, s.end+1)
}
func (s *subVector) Pop() Vector {
switch s.Len() {
case 0:
return nil
case 1:
return Empty
default:
return s.v.SubVector(s.begin, s.end-1)
}
}
func (s *subVector) SubVector(i, j int) Vector {
return s.v.SubVector(s.begin+i, s.begin+j)
}
func (s *subVector) Iterator() Iterator {
return newIteratorWithRange(s.v, s.begin, s.end)
}
type iterator struct {
v *vector
index int
end int
}
func newIterator(v *vector) *iterator {
return newIteratorWithRange(v, 0, v.Len())
}
func newIteratorWithRange(v *vector, begin, end int) *iterator {
it := &iterator{v, begin, end}
return it
}
func (it *iterator) Elem() interface{} {
if it.index >= len(it.v.nodes) {
return nil
}
return it.v.nodes[it.index]
}
func (it *iterator) HasElem() bool {
return it.index < it.end
}
func (it *iterator) Next() {
if it.index+1 >= len(it.v.nodes) {
it.index++
return
}
it.index++
}