
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


 
struct Queue{T}
    a::Array{T,1}
end
 
Queue() = Queue(Any[])
Queue(a::DataType) = Queue(a[])
Queue(a) = Queue(typeof(a)[])
 
Base.isempty(q::Queue) = isempty(q.a)
 
function Base.pop!(q::Queue{T}) where {T}
    !isempty(q) || error("queue must be non-empty")
    pop!(q.a)
end
 
function Base.push!(q::Queue{T}, x::T) where {T}
    pushfirst!(q.a, x)
    return q
end
 
function Base.push!(q::Queue{Any}, x::T) where {T}
    pushfirst!(q.a, x)
    return q
end
 