diff --git a/src/data-structures/queue/deque.ts b/src/data-structures/queue/deque.ts
index a730bcb..24eacaa 100644
--- a/src/data-structures/queue/deque.ts
+++ b/src/data-structures/queue/deque.ts
@@ -119,11 +119,11 @@ export class Deque<E> {
    */
   constructor(elements: IterableWithSizeOrLength<E> = [], bucketSize = (1 << 12)) {
 
-    let _size;
+    let _size: number;
     if ('length' in elements) {
-      _size = elements.length;
+      if (elements.length instanceof Function) _size = elements.length(); else _size = elements.length;
     } else {
-      _size = elements.size;
+      if (elements.size instanceof Function) _size = elements.size();else _size = elements.size;
     }
 
     this._bucketSize = bucketSize;
@@ -991,7 +991,7 @@ export class Deque<E> {
    * Time Complexity: O(1)
    * Space Complexity: O(1)
    */
-  
+
   /**
    * Time Complexity: O(1)
    * Space Complexity: O(1)
diff --git a/src/types/helpers.ts b/src/types/helpers.ts
index bb86b6c..39f75f1 100644
--- a/src/types/helpers.ts
+++ b/src/types/helpers.ts
@@ -16,11 +16,11 @@ export const enum IterateDirection {
 }
 
 export interface IterableWithSize<T> extends Iterable<T> {
-  size: number;
+  size: number | ((...args: any[]) => number);
 }
 
 export interface IterableWithLength<T> extends Iterable<T> {
-  length: number;
+  length: number | ((...args: any[]) => number);
 }
 
 export type IterableWithSizeOrLength<T> = IterableWithSize<T> | IterableWithLength<T>