Allocator abstract

abstract class Allocator

Annotations: @Since.new('2.12')

Manages memory on the native heap.

When allocating memory, prefer calling this allocator directly as a function (see AllocatorAlloc.call for details).

This interface provides only the allocate method to allocate a block of bytes, and the free method to release such a block again. Implementations only need to provide those two methods. The AllocatorAlloc.call extension method is defined in terms of those lower-level operations.

An example of an allocator wrapping another to count the number of allocations:

class CountingAllocator implements Allocator {
  final Allocator _wrappedAllocator;
  int _totalAllocations = 0;
  int _nonFreedAllocations = 0;

  CountingAllocator([Allocator? allocator])
      : _wrappedAllocator = allocator ?? calloc;

  int get totalAllocations => _totalAllocations;

  int get nonFreedAllocations => _nonFreedAllocations;

  @override
  Pointer<T> allocate<T extends NativeType>(int byteCount, {int? alignment}) {
    final result =
        _wrappedAllocator.allocate<T>(byteCount, alignment: alignment);
    _totalAllocations++;
    _nonFreedAllocations++;
    return result;
  }

  @override
  void free(Pointer<NativeType> pointer) {
    _wrappedAllocator.free(pointer);
    _nonFreedAllocations--;
  }
}

Available Extensions

• AllocatorAlloc

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

allocate()

Pointer<T> allocate<T extends NativeType>(int byteCount, {int? alignment})

Allocates byteCount bytes of memory on the native heap.

If alignment is provided, the allocated memory will be at least aligned to alignment bytes.

To allocate a multiple of sizeOf<T>() bytes, call the allocator directly as a function: allocator<T>(count) (see AllocatorAlloc.call for details).

// This allocates two bytes. If you intended two Int32's, this is an
// error.
allocator.allocate<Int32>(2);

// This allocates eight bytes, which is enough space for two Int32's.
// However, this is not the idiomatic way.
allocator.allocate<Int32>(sizeOf<Int32>() * 2);

// The idiomatic way to allocate space for two Int32 is to call the
// allocator directly as a function.
allocator<Int32>(2);

Throws an ArgumentError if the number of bytes or alignment cannot be satisfied.

Implementation

Pointer<T> allocate<T extends NativeType>(int byteCount, {int? alignment});

call() extension

Pointer<T> call<T extends SizedNativeType>([int count = 1])

Allocates sizeOf<T>() * count bytes of memory using allocate.

// This allocates eight bytes, which is enough space for two Int32's.
allocator<Int32>(2);

This extension method must be invoked with a compile-time constant T.

To allocate a specific number of bytes, not just a multiple of sizeOf<T>(), use allocate. To allocate with a non constant T, use allocate. Prefer call for normal use, and use allocate for implementing an Allocator in terms of other allocators.

Available on Allocator, provided by the AllocatorAlloc extension

Implementation

external Pointer<T> call<T extends SizedNativeType>([int count = 1]);

free()

void free(Pointer<NativeType> pointer)

Releases memory allocated on the native heap.

Throws an ArgumentError if the memory pointed to by pointer cannot be freed.

Implementation

void free(Pointer pointer);

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);

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);