This PR simplifies the PriorityQueue<TElement, TPriority>.UnorderedItemsCollection.Enumerator.MoveNext() implementation by merging the MoveNextRare helper method directly into MoveNext, following the pattern established by the recent improvement to List<T>.Enumerator. Additionally, it replaces manual exception throwing with ThrowHelper calls to improve method inlining performance.

Changes Made

• Merged MoveNextRare logic into MoveNext: The version validation and end-of-enumeration handling is now done directly in the main MoveNext method
• Removed the MoveNextRare helper method: No longer needed since its logic is integrated into MoveNext
• Simplified control flow: The method now checks version first (throwing on mismatch), then bounds, matching the pattern used in List<T>.Enumerator
• Improved inlining performance: Replaced manual throw new InvalidOperationException(SR.InvalidOperation_EnumFailedVersion) with System.Collections.ThrowHelper.ThrowVersionCheckFailed() calls in both MoveNext and Reset methods
• Consistent index handling: Changed _index = localQueue._size + 1 to _index = -1 to match the pattern used in List<T>.Enumerator

Before

public bool MoveNext()
{
    PriorityQueue<TElement, TPriority> localQueue = _queue;

    if (_version == localQueue._version && ((uint)_index < (uint)localQueue._size))
    {
        _current = localQueue._nodes[_index];
        _index++;
        return true;
    }

    return MoveNextRare();
}

private bool MoveNextRare()
{
    if (_version != _queue._version)
    {
        throw new InvalidOperationException(SR.InvalidOperation_EnumFailedVersion);
    }

    _index = _queue._size + 1;
    _current = default;
    return false;
}

After

public bool MoveNext()
{
    PriorityQueue<TElement, TPriority> localQueue = _queue;

    if (_version != localQueue._version)
    {
        System.Collections.ThrowHelper.ThrowVersionCheckFailed();
    }

    if ((uint)_index < (uint)localQueue._size)
    {
        _current = localQueue._nodes[_index];
        _index++;
        return true;
    }

    _current = default;
    _index = -1;
    return false;
}

Benefits

• Simplified code structure: Eliminates the helper method call overhead
• Consistent pattern: Matches the approach used in List<T>.Enumerator after its recent improvement, including the -1 index value for end-of-enumeration
• Maintained behavior: Preserves all existing functionality and error handling
• Better performance: Potential minor performance improvement by avoiding method calls in failure cases and better inlining characteristics through ThrowHelper usage

All existing tests pass (33,438 System.Collections tests), confirming the change maintains correctness while improving the implementation.

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.