concat.go

package flinx

// Append inserts an item to the end of a collection, so it becomes the last
// item.
func Append[T any](q Query[T], items ...T) Query[T] {

	length := len(items)
	var defaultValue T
	return Query[T]{
		Iterate: func() Iterator[T] {
			next := q.Iterate()
			index := 0

			return func() (T, bool) {
				i, ok := next()
				if ok {
					return i, ok
				}
				if index < length {
					idx := index
					index++

					return items[idx], true
				}

				return defaultValue, false
			}
		},
	}

}

// Concat concatenates two collections.
//
// The Concat method differs from the Union method because the Concat method
// returns all the original elements in the input sequences. The Union method
// returns only unique elements.
func Concat[T any](q, q2 Query[T]) Query[T] {
	return Query[T]{
		Iterate: func() Iterator[T] {
			next := q.Iterate()
			next2 := q2.Iterate()
			use1 := true

			return func() (item T, ok bool) {
				if use1 {
					item, ok = next()
					if ok {
						return
					}

					use1 = false
				}

				return next2()
			}
		},
	}

}

// Prepend inserts an item to the beginning of a collection, so it becomes the
// first item.
func Prepend[T any](q Query[T], items ...T) Query[T] {

	length := len(items)
	return Query[T]{
		Iterate: func() Iterator[T] {
			next := q.Iterate()
			index := 0

			return func() (T, bool) {
				if index < length {
					idx := index
					index++
					return items[idx], true

				}

				return next()
			}
		},
	}

}