
Data Structure

This illustrates a data structure, a means of storing data within a program.

You may see other such structures in the Data Structures category.
 Illustration of FIFO behavior
Task

Implement a FIFO queue.

Elements are added at one side and popped from the other in the order of insertion.



Operations:

   push   (aka enqueue)    - add element
   pop     (aka dequeue)    - pop first element
   empty                             - return truth value when empty


Errors:

   handle the error of trying to pop from an empty queue (behavior depends on the language and platform)


See

   Queue/Usage   for the built-in FIFO or queue of your language or standard library.


See also

 Array
 Associative array: Creation, Iteration
 Collections
 Compound data type
 Doubly-linked list: Definition, Element definition, Element insertion, List Traversal, Element Removal
 Linked list
 Queue: Definition, Usage
 Set
 Singly-linked list: Element definition, Element insertion, List Traversal, Element Removal
 Stack


const max_tail = 256
 
struct Queue<T> {
mut:
	data  []T
	tail int
	head  int
}
 
fn (mut queue Queue<T>) push(value T) {
	if queue.tail >= max_tail || queue.tail < queue.head {
		return
	}
	println('push: $value')
	queue.data << value
	queue.tail++
}
 
fn (mut queue Queue<T>) pop() !T {
	if queue.tail > 0 && queue.head < queue.tail {
		result := queue.data[queue.head]
		queue.head++
		println('Dequeue: top of Queue was $result')
		return result
	}
	return error('Queue Underflow!!')
}
 
fn (queue Queue<T>) peek() !T {
	if queue.tail > 0 && queue.head < queue.tail {
		result := queue.data[queue.head]
		println('Peek: top of Queue is $result')
		return result
	}
	return error('Out of Bounds...')
}
 
fn (queue Queue<T>) empty() bool {
	return queue.tail == 0
}
 
fn main() {
	mut queue := Queue<f64>{}
	println('Queue is empty? ' + if queue.empty() { 'Yes' } else { 'No' })
	queue.push(5.0)
	queue.push(4.2)
	println('Queue is empty? ' + if queue.empty() { 'Yes' } else { 'No' })
	queue.peek() or { return }
	queue.pop() or { return }
	queue.pop() or { return }
	queue.push(1.2)
}