==Introduction==

A //Containers// is a general name for data structures intended to hold group of elements of certain type.
Considering that almost every program needs containers to store, retrieve, search or otherwise process aggregate data,  
obviously efficiency of containers implementation is one of the top priorities for Xreate design.

Main idea behind containers in Xreate is to gather information on //how containers are used//, inferred  from program sources.
On this ground it's possible to choose semi-automatically most appropriate data structure for container implementation to efficiently fullfil particular needs.

    a= [1, 2, 3, 4, 5]::    [num]; impl(solid).      //container definition
    
    b= a[0]::   num; op(randaccess).            //operation on container

In this example, definition of container(variable `a`) offers one or several implementations it supports, that is `impl(solid)` which
is explicilty provided for clarity.  On the other side, //retrieving by index// operation(variable `b`) demands certain implementations
to operate. Annotation `op(randaccess)` explicitly describes operation nature, i.e. it requires any data structure that supports //random access// .
Based on gathered information, most appropriate tradeoff //in supply and demand// is applied as given container implementation, i.e. `impl(solid)` in this simple case.

In order to exppress possible and required implementations, describe operations, constraints and preferences an annotations are used, either manually provided or automatically inferred from program sources.

==Container definitions==



==Container operations==

| `map` loop  | `op(seqaccess)` | `impl(on_the_fly)`, `impl(solid)`
| `fold` loop | `op(seqaccess)`| `impl(on_the_fly)`, `impl(solid)`
| index retrieving | `op(randaccess` | `impl(solid)`