Documentation: CustomChannelFieldSizeAttribute.cs

1. Purpose

This module provides a mechanism for associating fixed size metadata with enum values (specifically MMETables.MMEPossibleChannelsFields), enabling retrieval of custom field sizes via reflection. It exists to decouple size configuration from business logic, allowing channel field sizes to be defined declaratively as attributes on enum members rather than hard-coded elsewhere.

2. Public Interface

`CustomChannelFieldSizeAttribute` (Class)

A custom attribute that stores an integer size value.

Member	Signature	Description
Constructor	`internal CustomChannelFieldSizeAttribute(int size)`	Creates an instance with the specified size. Note: Internal access only.
Property	`public int Size { get; private set; }`	Gets the size value. Read-only after construction.

`CustomChannelFieldSizeExtensions` (Static Class)

Provides helper methods for retrieving field sizes.

Method	Signature	Description
`GetFieldSize`	`public static int GetFieldSize(MMETables.MMEPossibleChannelsFields field)`	Retrieves the `Size` value from the `CustomChannelFieldSizeAttribute` applied to the given enum value. Not an extension method—must be called statically.

`EnumExtensions` (Static Class)

Provides generic reflection-based attribute retrieval for enum values.

Method	Signature	Description
`GetAttribute<TAttribute>`	`public static TAttribute GetAttribute<TAttribute>(this Enum value) where TAttribute : Attribute`	Extension method that retrieves a single custom attribute of type `TAttribute` from the given enum value. Returns `null` if not found; throws `InvalidOperationException` if multiple matching attributes exist.

3. Invariants

Attribute Application: GetFieldSize assumes that CustomChannelFieldSizeAttribute is always applied to the passed MMEPossibleChannelsFields enum value. If the attribute is missing, a NullReferenceException will occur.
Single Attribute Constraint: GetAttribute<TAttribute> uses SingleOrDefault(), enforcing that at most one attribute of a given type may be present on any enum value. Multiple attributes of the same type will cause an InvalidOperationException.
Immutability: The Size property is set only at construction and cannot be modified thereafter (private setter).
Construction Restriction: The attribute constructor is internal, meaning attributes can only be defined within the same assembly.

4. Dependencies

This module depends on:

System (for Attribute, Enum, Type reflection APIs)
System.Linq (for OfType<T>(), SingleOrDefault())
MMETables.MMEPossibleChannelsFields — an external enum type that this module is designed to annotate. Location/assembly not visible in source.

What depends on this module:

Cannot be determined from source alone. Consumers would be any code that needs to retrieve field sizes for MMEPossibleChannelsFields enum values.

5. Gotchas

GetFieldSize is NOT an extension method — Despite being defined in a class named CustomChannelFieldSizeExtensions, the method lacks the this keyword on its parameter. It must be called as CustomChannelFieldSizeExtensions.GetFieldSize(field), not field.GetFieldSize().
Potential NullReferenceException — GetFieldSize directly accesses .Size on the result of GetAttribute<CustomChannelFieldSizeAttribute>() without null-checking. If the enum value lacks this attribute, the method will throw.
Internal constructor limits extensibility — The internal constructor means consumers outside this assembly cannot create new instances of CustomChannelFieldSizeAttribute. This is likely intentional to control where/how the attribute is applied, but could be restrictive for testing or extension scenarios.
Tight coupling to specific enum type — GetFieldSize is hardcoded to MMETables.MMEPossibleChannelsFields, making this utility non-reusable for other enums even though GetAttribute<T> is generic.

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