Stack

General

Stack is a built-in collection class in Ysharp that implements a last-in, first-out (LIFO) data structure. Elements are added and removed from the top of the stack.

Stack extends the vector protocol, meaning it also supports iteration via foreach.

Note
Some methods have aliases for convenience. For example, push is an alias for add, top is an alias for peek, and isEmpty is an alias for empty.

var stack = new Stack();

Creates a new, empty Stack instance.

Example

var stack = new Stack();

stack.push(1);
stack.push(2);
stack.push(3);

println stack.peek();   // 3
println stack.pop();    // 3
println stack.size();   // 2

Reference

Instance methods

Method	Signature	Return Type	Description
add / push	stack.add(value : any)	int	Pushes a value onto the stack and returns the new size
addAll	stack.addAll(collection : Collection)	int	Adds all elements from the given collection (Stack, Array, Queue, Set, PriorityQueue) to this stack and returns the new size
pop	stack.pop()	any	Removes and returns the top element; throws if empty
peek / top	stack.peek()	any	Returns the top element without removing it; throws if empty
peekOrNull	stack.peekOrNull()	any | null	Returns the top element or null if the stack is empty
empty / isEmpty	stack.empty()	bool	Returns true if the stack is empty
size	stack.size()	int	Returns the number of elements in the stack
contains	stack.contains(value : any)	bool	Returns true if the stack contains the given value
search	stack.search(value : any)	int	Returns 1-based position from the top, or -1 if not found
clear	stack.clear()	null	Removes all elements from the stack
clone	stack.clone()	Stack	Returns a shallow copy of the stack
reverse	stack.reverse()	Stack	Returns a new stack with elements in reversed order
toArray / toList	stack.toArray()	Array	Returns an array containing all elements in stack order
asQueryable	stack.asQueryable()	Queryable	Converts the stack into a queryable sequence (LINQ-style operations)
toString	stack.toString()	string	Returns a string representation of the stack

add(value : any) : int

push(value : any) : int

• Pushes a value onto the stack and returns the new size

var stack = new Stack();

stack.push(10);
stack.push(20);

println stack.size(); // 2
println stack.peek(); // 20

addAll(collection : Collection) : int

• Adds all elements from the given collection (Stack, Array, Queue, Set, PriorityQueue) to this stack and returns the new size

var stack = new Stack();
var arr = [1,2,3];

stack.addAll(arr);

println stack.size(); // 3
println stack.peek(); // 3

pop() : any

• Removes and returns the top element; throws if empty

var stack = new Stack();

stack.push(10);
stack.push(20);

println stack.pop(); // 20
println stack.size(); // 1

// pop on empty
stack.pop();
try do
    stack.pop();
end
catch(e) do
    println e;
end

peek() : any

top() : any

• Returns the top element without removing it; throws if empty

var stack = new Stack();

stack.push(10);
stack.push(20);

println stack.peek(); // 20
println stack.top();  // 20
println stack.size(); // 2 (unchanged)

// peek on empty
var emptyStack = new Stack();

try do
    emptyStack.peek();
end
catch(e) do
    println e;
end

empty() : bool

isEmpty() : bool

• Returns true if the stack is empty

var stack = new Stack();

println stack.empty();   // true
println stack.isEmpty(); // true

stack.push(10);

println stack.empty();   // false
println stack.isEmpty(); // false

stack.pop();

println stack.empty();   // true

size() : int

• Returns the number of elements in the stack

var stack = new Stack();

println stack.size(); // 0

stack.push(10);
stack.push(20);

println stack.size(); // 2

stack.pop();

println stack.size(); // 1

search(value : any) : int

• Returns 1-based position from the top, or -1 if not found

var stack = new Stack();

stack.push(10);
stack.push(20);
stack.push(30); // top

println stack.search(30); // 1
println stack.search(20); // 2
println stack.search(10); // 3
println stack.search(99); // -1

clear() : null

• Removes all elements from the stack

var stack = new Stack();

stack.push(10);
stack.push(20);

println stack.size(); // 2

stack.clear();

println stack.size();   // 0
println stack.isEmpty(); // true

// accessing after clear
println stack.peekOrNull(); // null

clone() : Stack

• Returns a shallow copy of the stack

var stack = new Stack();

stack.push(10);
stack.push(20);
stack.push(30);

var cloned = stack.clone();

println cloned.size(); // 3
println cloned.peek(); // 30

// modify clone
cloned.pop();

println cloned.size(); // 2
println stack.size();  // 3 (original unchanged)

reverse() : Stack

• Returns a new stack with elements in reversed order

var stack = new Stack();

stack.push(10);
stack.push(20);
stack.push(30); // top

var reversed = stack.reverse();

println reversed.pop(); // 10
println reversed.pop(); // 20
println reversed.pop(); // 30

// original unchanged
println stack.peek(); // 30

toArray() : Array

toList() : Array

• Returns an array containing all elements in stack order

var stack = new Stack();

stack.push(10);
stack.push(20);
stack.push(30);

var arr = stack.toArray();

println arr.size();   // 3
println arr.get(0);   // 10
println arr.get(1);   // 20
println arr.get(2);   // 30

asQueryable() : Queryable

• Converts the stack into a queryable sequence (LINQ-style operations)

var stack = new Stack();

stack.push(1);
stack.push(2);
stack.push(3);

var q = stack.asQueryable();

// example query (assuming LINQ-style API)
var result = q
    .where((x, a, b) => x > 1)
    .select((x, a, b) => x * 10)
    .toArray();

println result.get(0); // 20
println result.get(1); // 30

toString() : string

• Returns a string representation of the stack

var stack = new Stack();

stack.push(10);
stack.push(20);
stack.push(30);

println stack.toString(); // [ 10, 20, 30 ]