Splittable Concept


Requirements for a type whose instances can be split into two pieces.


The following table lists the requirements for a splittable type X with instance x.

Splittable Concept



X::X(X& x, split)

Split x into x and newly constructed object.


A type is splittable if it has a splitting constructor that allows an instance to be split into two pieces. The splitting constructor takes as arguments a reference to the original object, and a dummy argument of type split, which is defined by the library. The dummy argument distinguishes the splitting constructor from a copy constructor. After the constructor runs, x and the newly constructed object should represent the two pieces of the original x. The library uses splitting constructors in two contexts:

  • Partitioning a range into two subranges that can be processed concurrently.
  • Forking a body (function object) into two bodies that can run concurrently.

Range classes might additionally define an optional proportional splitting constructor, distinguished by an argument of type proportional_split. See the proportional_split Class and blocked_range Template Class sections for more info.

The following model types provide examples.

Model Types

blocked_range and blocked_range2d represent splittable ranges. For each of these, splitting partitions the range into two subranges. See the blocked_range Template Class section for an example of the splitting constructor for blocked_range.

The bodies for parallel_reduce and parallel_scan must be splittable. For each of these, splitting results in two bodies that can be run concurrently.

For more complete information about compiler optimizations, see our Optimization Notice.