stride3d/stride · error · ArgumentOutOfRangeException

Invalid existing index

Q: What causes "Invalid existing index {index} for source length {sourceLength}" in stride3d/stride?

Validate 0 <= i < deque.Count before RemoveAt

Error message

Invalid existing index {index} for source length {sourceLength}

What it means

Thrown by CheckExistingIndexArgument when an index meant to address an EXISTING element falls outside [0, sourceLength-1]. Unlike insertion indices, an existing-element index may not equal Count. Raised from RemoveAt (and validated on construction) as ArgumentOutOfRangeException naming 'index'.

Solutions

Validate 0 <= i < deque.Count before RemoveAt
Re-fetch Count immediately before each removal inside loops
Guard against an empty deque before removing by index

Example fix

// before
for (int i = 0; i <= deque.Count; i++) deque.RemoveAt(i); // throws at i == Count
// after
for (int i = deque.Count - 1; i >= 0; i--) deque.RemoveAt(i);

Defensive patterns

Strategy: validation

Validate before calling

if (index < 0 || index >= deque.Count) throw new ArgumentOutOfRangeException(nameof(index), $"Index {index} invalid for Count {deque.Count}");
deque.RemoveAt(index);

Prevention

Remember existing-element indices max out at Count-1
Re-fetch Count each iteration of removal loops
Never reuse indices captured before mutations

When it happens

Trigger: Calling deque.RemoveAt(i) where i < 0 or i >= Count.

Common situations: Looping with i <= Count instead of i < Count; removing from an empty deque (any index is invalid); a stale index captured before other removals shrank the deque.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/9a9ccc038e395769. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core/Collections/Dequeue.cs:405

    private static void CheckNewIndexArgument(int sourceLength, int index)
    {
        if (index < 0 || index > sourceLength)
        {
            throw new ArgumentOutOfRangeException(nameof(index), "Invalid new index " + index + " for source length " + sourceLength);
        }
    }

    /// <summary>
    /// Checks the <paramref name="index"/> argument to see if it refers to an existing element in a source of a given length.
    /// </summary>
    /// <param name="sourceLength">The length of the source. This parameter is not checked for validity.</param>
    /// <param name="index">The index into the source.</param>
    /// <exception cref="ArgumentOutOfRangeException"><paramref name="index"/> is not a valid index to an existing element for the source.</exception>
    private static void CheckExistingIndexArgument(int sourceLength, int index)
    {
        if (index < 0 || index >= sourceLength)
        {
            throw new ArgumentOutOfRangeException(nameof(index), "Invalid existing index " + index + " for source length " + sourceLength);
        }
    }

    /// <summary>
    /// Checks the <paramref name="offset"/> and <paramref name="count"/> arguments for validity when applied to a source of a given length. Allows 0-element ranges, including a 0-element range at the end of the source.
    /// </summary>
    /// <param name="sourceLength">The length of the source. This parameter is not checked for validity.</param>
    /// <param name="offset">The index into source at which the range begins.</param>
    /// <param name="count">The number of elements in the range.</param>
    /// <exception cref="ArgumentOutOfRangeException">Either <paramref name="offset"/> or <paramref name="count"/> is less than 0.</exception>
    /// <exception cref="ArgumentException">The range [offset, offset + count) is not within the range [0, sourceLength).</exception>
    private static void CheckRangeArguments(int sourceLength, int offset, int count)
    {
        if (offset < 0)
        {
            throw new ArgumentOutOfRangeException(nameof(offset), "Invalid offset " + offset);
        }

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