stride3d/stride · error · ArgumentException

Expecting length >= 2 and at least a special character '.'…

Error message

Expecting length >= 2 and at least a special character '.', '~', '-' (not starting on first char for '-')

What it means

SpecialCollectionMember must be a string of length >= 2 containing at least one of the characters '.', '~', or '-' (with '-' not allowed as the first character), because the value is interpreted as a qualified member pattern rather than a plain name. Plain names or too-short strings throw ArgumentException.

Solutions

Use the fully qualified form including a type separator, e.g. "MyNamespace.MyType~MyCollection" or "MyNamespace.MyType.Member"
Ensure length >= 2 and that '-' is not the first character

Example fix

// before
settings.SpecialCollectionMember = "Items";
// after
settings.SpecialCollectionMember = "MyApp.Model.MyType~Items";

Defensive patterns

Strategy: validation

Validate before calling

bool IsValidSpecialMember(string v) => v != null && v.Length >= 2 && (v.Contains(".") || v.Contains("~") || v.IndexOf('-') > 0);
if (!IsValidSpecialMember(memberName)) throw new FormatException($"{memberName} is not a qualified special collection member");

Type guard

bool IsValidSpecialMember(string v) => v != null && v.Length >= 2 && (v.Contains(".") || v.Contains("~") || v.IndexOf('-') > 0);

Try / catch

try { settings.SpecialCollectionMember = memberName; } catch (ArgumentException ex) { throw new FormatException("Invalid SpecialCollectionMember", ex); }

Prevention

Always use fully qualified member patterns (Type.Member or Type~Member)
Never assign bare property names or single characters

When it happens

Trigger: Setting SpecialCollectionMember to values like "x", "items", "a-", or any string lacking '.', '~' and a non-initial '-'.

Common situations: Typing a bare property name instead of the fully qualified pattern; trimming/cleaning config values so separators are lost.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/e914ec762baff00e. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core.Yaml/Serialization/SerializerSettings.cs:256

        /// <exception cref="System.ArgumentNullException">value</exception>
        /// <exception cref="System.ArgumentException">Expecting length >= 2 and at least a special character '.', '~', '-' (not starting on first char for '-')</exception>
        /// <remarks>A pure <see cref="System.Collections.IDictionary" /> or <see cref="System.Collections.ICollection" /> is a class that inherits from these types but are not adding any
        /// public properties or fields. When these types are pure, they are respectively serialized as a YAML mapping (for dictionary) or a YAML sequence (for collections).
        /// If the collection type to serialize is not pure, the type is serialized as a YAML mapping sequence that contains the public properties/fields as well as a
        /// special fielx (e.g. "~Items") that contains the actual items of the collection (either a mapping for dictionary or a sequence for collections).
        /// The <see cref="SpecialCollectionMember" /> is this special key that is used when serializing items of a non-pure collection.</remarks>
        public string SpecialCollectionMember
        {
            get { return specialCollectionMember; }
            set
            {
                if (value == null)
                    throw new ArgumentNullException("value", $"{nameof(specialCollectionMember)} can not be null");

                // TODO this is a poor check. Need to verify this against the specs
                if (value.Length < 2 || !(value.Contains(".") || value.Contains("~") || value.IndexOf('-') > 0))
                {
                    throw new ArgumentException(
                        "Expecting length >= 2 and at least a special character '.', '~', '-' (not starting on first char for '-')");
                }

                specialCollectionMember = value;
            }
        }

        /// <summary>
        /// Gets the attribute registry.
        /// </summary>
        /// <value>The attribute registry.</value>
        public IAttributeRegistry Attributes
        {
            get { return attributeRegistry; }
            set
            {
                if (value == null)
                    throw new ArgumentNullException("value", $"{nameof(Attributes)} can not be null");

View on GitHub (pinned to 96fad776d2)