The array to partition. This parameter is not marked 'ref' to allow temporary slices to be sorted. As buf is not resized in any way, omitting the 'ref' qualifier has no effect on the result of this operation, even though it may be viewed as a side-effect.
The evaluation predicate, which should return true if the element satisfies the condition and false if not. This predicate may be any callable type.
The number of elements that satisfy pred.
Partitions buf such that all elements that satisfy pred will be placed before the elements that do not satisfy pred. The algorithm is not required to be stable.