Collector<T, A, R> class

A mutable reduction operation that accumulates input elements into a mutable result container, optionally transforming the accumulated result into a final representation after all input elements have been processed.

Reduction operations can be performed either sequentially or in parallel.

Examples of mutable reduction operations include: accumulating elements into a List; concatenating strings using a StringBuffer; computing summary information about elements such as sum, min, max, or average; computing "pivot table" summaries such as "maximum valued transaction by seller", etc.

Example

final collector = Collector<String, StringBuffer, String>(
  supplier: () => StringBuffer(),
  accumulator: (buffer, element) => buffer.write(element),
  combiner: (buffer1, buffer2) => buffer1..write(buffer2.toString()),
  finisher: (buffer) => buffer.toString(),
);
Annotations

Constructors

Collector({required A supplier(), required void accumulator(A, T), required A combiner(A, A), required R finisher(A)})
Creates a new Collector with the specified functions.
const

Properties

accumulator → void Function(A, T)
A function that folds a value into a mutable result container.
final
combiner → A Function(A, A)
A function that accepts two partial results and merges them.
final
finisher → R Function(A)
A function that transforms the intermediate accumulation result into the final result type.
final
hashCode → int
The hash code for this object.
no setterinherited
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited
supplier → A Function()
A function that creates and returns a new mutable result container.
final

Methods

noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
toString() → String
A string representation of this object.
inherited

Operators

operator ==(Object other) → bool
The equality operator.
inherited