use Collection;


import Collection;

Provides an abstract class representing a ‘Collection’ interface.


A ‘Collection’ is an interface for a data structure that is a ‘contract’ between the user and implementer that it fulfills the following:

  1. Is safe parallel-safe, hence is safe to use across multiple tasks across multiple locales.

  2. Supports the basic operations that any data structure needs to be truly useful, that is:

  1. Insertion of an arbitrary element. From this, we can insert bulk arbitrary elements.

  2. Removal of an arbitrary element. From this, we can remove bulk arbitrary elements.

  3. Iteration over all elements. From this, we can perform lookups over all elements.

From the standpoint of the user, who directly benefits, they obtain a very nice but minimal guarantee on the object they are using, and from the implementor’s view, they get to the benefit from both implementing a well-design interface, and from getting some utility methods ‘for-free’.


This module is a work in progress and may change in future releases.

Bugs and Known Issues

  1. Parallel iteration is not apart of the core Collections module as currently the Chapel compiler will produce an internal error. As such, the utility methods provided ‘for-free’ use serial iteration. This issue has been documented under issue #6998 . Couple this fact with the fact that break ing out of a serial iterator will result in resource leakage, where destructors are not called, hence Collections using some RAII-based resource cleanup will end up leaking and potentially leaving the Collection in an undefined state. This has been documented under issue #6912 .


class CollectionImpl
type eltType

The type of element that this Collection holds.

proc init(type eltType)
proc add(elt: eltType) : bool

Adds an element to this data structure.

proc addBulk(elts) : int

Add all elements in bulk to this data structure. If the data structure rejects an element, we cease to offer more. We return the number of elements successfully added to this data structure.

proc remove() : (bool, eltType)

Removes an arbitrary element from this data structure.

proc removeBulk(nElts: int)

Removes nElts elements from this data structure, returning them as an array. If the data structure fails to produce a new element, we cease and shrink the array to its appropriate size and return that.

proc contains(elt: eltType) : bool

Determine whether an element exists in this collection.

proc clear()

Clears all elements in this collection.

proc isEmpty() : bool

Check if this data structure is empty.

proc size : int

Syntactic sugar for getSize.

proc getSize() : int

Obtain the number of elements contained in this collection.

iter these() : eltType

Iterate over all elements in the data structure.

operator CollectionImpl.+=(ref c: CollectionImpl(?eltType), elt: eltType)

Syntactic sugar for CollectionImpl.add.