clockworklabs/SpacetimeDB · error · ArgumentException

Argument must be a I256

Error message

Argument must be a I256

What it means

I256 is the SpacetimeDB BSATN.Runtime 256-bit signed integer type. Its untyped IComparable.CompareTo(object?) overload accepts only another I256 or null; any other runtime type throws ArgumentException because ordering across unrelated types is undefined.

Solutions

1. Call the typed CompareTo(I256) overload or use the comparison operators
2. Convert or pattern-match the other operand to I256 before comparing
3. Keep collections homogeneous (I256[]) or pass a custom comparer

Example fix

// before
object x = someI128;
int cmp = i256.CompareTo(x); // ArgumentException: Argument must be a I256

// after
int cmp = i256.CompareTo((I256)x); // only after verifying/casting the type

static bool CanCompareWithI256(object? other) => other is null || other is SpacetimeDB.I256;

static bool IsI256(object? value) => value is SpacetimeDB.I256;

try
{
    var cmp = ((IComparable)i256Value).CompareTo(boxed);
}
catch (ArgumentException)
{
    // convert operand to I256 or reject the mixed comparison
}

When it happens

Trigger: Calling CompareTo(object?) with a boxed value that is not an I256 — e.g. an I128, BigInteger, long, or string — via Array.Sort, ArrayList, or manual object comparisons.

Common situations: Comparing Identity-sized values pulled out of object-typed collections; mixed numeric sorts; ported code that previously compared BigInteger with other numerics.

Related errors

• Argument must be a I128
• Argument must be a U128
• Argument must be a U256
• Argument must be a ConnectionId
• Argument must be a Identity

AI-assisted analysis of clockworklabs/SpacetimeDB@6dee26c6ef (2026-08-20). Data as JSON: /api/errors/ba253d7136b0976d. Report an issue: GitHub.

Appendix: source

Thrown at crates/bindings-csharp/BSATN.Runtime/BSATN/I256.cs:50

    internal U128 Lower => _lower;

    internal U128 Upper => _upper;

    /// <inheritdoc cref="IComparable.CompareTo(object)" />
    public int CompareTo(object? value)
    {
        if (value is I256 other)
        {
            return CompareTo(other);
        }
        else if (value is null)
        {
            return 1;
        }
        else
        {
            throw new ArgumentException("Argument must be a I256", nameof(value));
        }
    }

    /// <inheritdoc cref="IComparable{T}.CompareTo(T)" />
    public int CompareTo(I256 value)
    {
        if (this < value)
        {
            return -1;
        }
        else if (this > value)
        {
            return 1;
        }
        else
        {
            return 0;
        }

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