deafult-dict-granular.php

<?php

class DefaultDict implements DimensionFetchable, DimensionWritable, FetchAppendable, DimensionUnsettable
{
    private array $backingDict = [];

    /**
     * @param callable $factory Callback to provide a default value on read
     */
    public function __construct(
        private $factory
    ) {}

    public function offsetGet(mixed $offset): mixed
    {
        if ( ! array_key_exists(array: $this->backingDict, key: $offset) ) {
            // Calculate the default, but don't save it
            return ($this->factory)($offset);
        }

        return $this->backingDict[$offset];
    }

    public function &offsetFetch(mixed $offset): mixed
    {
        if ( ! array_key_exists(array: $this->backingDict, key: $offset) ) {
            // Populate the default value and return it by reference
            $this->backingDict[$offset] = ($this->factory)($offset);
        }

        return $this->backingDict[$offset];
    }

    public function offsetExists(mixed $offset): bool
    {
        return array_key_exists(array: $this->backingDict, key: $offset);
    }

    public function offsetSet(mixed $offset, mixed $value): void
    {
        $this->backingDict[$offset] = $value;
    }

    public function offsetUnset(mixed $offset): void
    {
        unset($this->backingDict[$offset]);
    }

    public function append(mixed $value): void
    {
        $this->backingDict[] = $value;
    }

    public function &fetchAppend(): mixed
    {
        // First, get an append-reference on the actual array
        $newItem =& $this->backingDict[];
        // Next, generate a default value for it
        $newItem = ($this->factory)(null);
        // Finally, return it, and let the engine decide if it's a useful value for the operation
        return $newItem;
    }
}