Returns the number of items currently in the container.
| size < abstract-bag/set-container > | 
| size < alist-container > | 
| size < array > | 
| size < bag/set-container > | 
| size < cl-graph:basic-graph > | 
| size < basic-queue > | 
| size < binary-search-tree > | 
| size < bst-node > | 
| size < contents-as-array-mixin > | 
| size < contents-as-hashtable-mixin > | 
| size < contents-as-sequence-mixin > | 
| size < dlist-container > | 
| size < hash-table > | 
| size < list > | 
| size < package-container > | 
| size < priority-queue-on-container > | 
| size < quad-tree > | 
| size < ring-buffer > | 
| size < stable-associative-container > | 
| size < stack-container > | 
| size < vector > | 
| size < vector-container > |