AttributeExtensions

Purpose

Convenience extension methods for discovering and extracting custom attribute instances and values from Type and MemberInfo using System.Reflection.

These wrappers reduce boilerplate by performing casting and null-checks and by returning default values when attributes are not present.

When to Use

• When you need to read attribute instances or values from types, methods, properties, fields, or other members via reflection.
• When you want compact, null-safe attribute value extraction without repeated GetCustomAttributes(...).OfType<T>().FirstOrDefault() code.

API Reference

• TAttribute? GetCustomAttribute<TAttribute>(this Type @this, BindingFlags flags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic) where TAttribute : Attribute
  • Returns the first attribute of type TAttribute applied to the Type, or null if not found.
• TAttribute? GetCustomAttribute<TAttribute>(this MemberInfo @this, BindingFlags flags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic) where TAttribute : Attribute
  • Returns the first attribute of type TAttribute applied to the MemberInfo, or null if not found.
• TResult GetCustomAttributeValue<TAttribute, TResult>(this Type @this, Func<TAttribute, TResult> selector, TResult defaultValue = default, BindingFlags flags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic) where TAttribute : Attribute
  • Finds the first attribute of type TAttribute on the Type and returns the projected value via selector, or defaultValue when the attribute is missing.
• TResult GetCustomAttributeValue<TAttribute, TResult>(this MemberInfo @this, Func<TAttribute, TResult> selector, TResult defaultValue = default, BindingFlags flags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic) where TAttribute : Attribute
  • Same as above for MemberInfo.

How to Use

• To test presence of an attribute:

var has = typeof(MyClass).GetCustomAttribute<ObsoleteAttribute>() != null;

• To get an attribute value with a safe fallback:

var msg = typeof(MyClass).GetCustomAttributeValue<ObsoleteAttribute, string>(a => a.Message, "");

Examples

[Obsolete("Use NewClass instead")]
public class OldClass { }

var attr = typeof(OldClass).GetCustomAttribute<ObsoleteAttribute>();
Console.WriteLine(attr?.Message); // "Use NewClass instead"

var message = typeof(OldClass).GetCustomAttributeValue<ObsoleteAttribute, string>(a => a.Message, "No message");
Console.WriteLine(message); // "Use NewClass instead"

Remarks

• The flags parameter is currently not used in the implementation but is retained for API compatibility; passing different binding flags has no effect.
• These helpers return null or default when attributes are missing — prefer this behavior for concise call sites.
• For performance-sensitive loops, consider caching attribute lookups.

---

Documentation mirrors the helper implementations in AttributeExtensions.cs in the source tree.