Order<A> abstract

abstract class Order<A>

Defines a total ordering for elements of type A.

Orders are most commonly used for sorting elements, but can be useful for other purposes.

Constructors

Order() const

const Order()

Implementation

const Order();

Order.from() factory

factory Order.from(int Function(A, A) f)

Creates a new Order that compares 2 elements using f.

Implementation

factory Order.from(Function2<A, A, int> f) => _OrderF(f);

Order.fromLessThan() factory

factory Order.fromLessThan(bool Function(A, A) cmp)

Creates a new Order from a less-than predicate cmp.

Returns -1 if cmp(x, y), 1 if cmp(y, x), and 0 otherwise.

Implementation

factory Order.fromLessThan(Function2<A, A, bool> cmp) {
  return Order.from((x, y) {
    if (cmp(x, y)) {
      return -1;
    } else if (cmp(y, x)) {
      return 1;
    } else {
      return 0;
    }
  });
}

Properties

hashCode no setter inherited

int get hashCode

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Inherited from Object.

Implementation

external int get hashCode;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

Methods

compare()

int compare(A x, A y)

Compares to instances and returns:

• < 0: If x is considered to be less than y
• 0: If x is considered to be equal to y

0: If x is considered to be greater than y

Implementation

int compare(A x, A y);

contramap()

Order<B> contramap<B>(A Function(B) f)

Returns a new Order for type B by first transforming values with f and then comparing them using this Order.

Implementation

Order<B> contramap<B>(Function1<B, A> f) => _OrderF((x, y) => compare(f(x), f(y)));

eqv()

bool eqv(A x, A y)

Returns true if x is equal to y, as defined by this Order. Otherwise, false is returned.

Implementation

bool eqv(A x, A y) => compare(x, y) == 0;

gt()

bool gt(A x, A y)

Returns true if x is greater than y, as defined by this Order. Otherwise, false is returned.

Implementation

bool gt(A x, A y) => compare(x, y) > 0;

gteqv()

bool gteqv(A x, A y)

Returns true if x is greater than or equal to y, as defined by this Order. Otherwise, false is returned.

Implementation

bool gteqv(A x, A y) => compare(x, y) >= 0;

isReverseOf()

bool isReverseOf(Order<A> other)

Returns true if other is the reverse of this Order.

Implementation

bool isReverseOf(Order<A> other) => switch (other) {
  _ReverseOrder(:final outer) => outer == this,
  _ => false,
};

lt()

bool lt(A x, A y)

Returns true if x is less than y, as defined by this Order. Otherwise, false is returned.

Implementation

bool lt(A x, A y) => compare(x, y) < 0;

lteqv()

bool lteqv(A x, A y)

Returns true if x is less than or equal to y, as defined by this Order. Otherwise, false is returned.

Implementation

bool lteqv(A x, A y) => compare(x, y) <= 0;

max()

A max(A x, A y)

Returns the greater of x and y, as defined by this Order.

Implementation

A max(A x, A y) => gt(x, y) ? x : y;

min()

A min(A x, A y)

Returns the lesser of x and y, as defined by this Order.

Implementation

A min(A x, A y) => lt(x, y) ? x : y;

neqv()

bool neqv(A x, A y)

Returns false if x is equal to y, as defined by this Order. Otherwise, true is returned.

Implementation

bool neqv(A x, A y) => !eqv(x, y);

noSuchMethod() inherited

dynamic noSuchMethod(Invocation invocation)

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

Implementation

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

reverse()

Order<A> reverse()

Returns a new Order that reverses the evaluation of this Order.

Implementation

Order<A> reverse() => _OrderF((a, b) => compare(b, a));

toString() inherited

String toString()

A string representation of this object.

Some classes have a default textual representation, often paired with a static parse function (like int.parse). These classes will provide the textual representation as their string representation.

Other classes have no meaningful textual representation that a program will care about. Such classes will typically override toString to provide useful information when inspecting the object, mainly for debugging or logging.

Inherited from Object.

Implementation

external String toString();

Operators

operator ==() inherited

bool operator ==(Object other)

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

Inherited from Object.

Implementation

external bool operator ==(Object other);

Static Properties

doubles final

final Order<double> doubles

Order for double type.

Implementation

static final doubles = Order.fromComparable<double>();

ints final

final Order<int> ints

Order for int type.

Implementation

static final ints = Order.fromComparable<int>();

strings final

final Order<String> strings

Order for String type.

Implementation

static final strings = Order.fromComparable<String>();

Static Methods

by()

Order<A> by<A, B extends Comparable>(B Function(A) f)

Creates a new Order for type A by applying f to and instances and comparing the resulting Comparable.

Implementation

static Order<A> by<A, B extends Comparable<dynamic>>(Function1<A, B> f) =>
    Order.from((a, b) => f(a).compareTo(f(b)));

fromComparable()

Order<A> fromComparable<A extends Comparable>()

Creates a new Order that uses the Comparable.compareTo defined for the given type.

Implementation

static Order<A> fromComparable<A extends Comparable<dynamic>>() =>
    Order.from((A a, A b) => a.compareTo(b));

fromOrdered()

Order<A> fromOrdered<A extends Ordered>()

Creates a new Order that uses the Ordered.compareTo defined for the given type.

Implementation

static Order<A> fromOrdered<A extends Ordered<dynamic>>() =>
    Order.from((A a, A b) => a.compareTo(b));

whenEqual()

Order<A> whenEqual<A>(Order<A> first, Order<A> second)

Returns an Order that first compares by first, and breaks ties using second.

Implementation

static Order<A> whenEqual<A>(Order<A> first, Order<A> second) => Order.from((x, y) {
  final c = first.compare(x, y);
  return c == 0 ? second.compare(x, y) : c;
});