Compare ArrayString<T> and ArraySegment<T> from .NET

[konard]

📋 Issue Reference

Fixes #102

🔍 Analysis Summary

This PR provides a comprehensive comparison between Platform.Collections' ArrayString<T> and .NET's ArraySegment<T>. Both types serve similar purposes but have important architectural and behavioral differences.

🏗️ Key Architectural Differences

Type Design

• ArrayString: Reference type (class) inheriting from Segment<T>
• ArraySegment: Value type (struct) from .NET BCL

Constructors

• ArrayString:
  • new ArrayString<T>(length) - Creates new array
  • new ArrayString<T>(array) - Wraps entire array from index 0
  • new ArrayString<T>(array, length) - Wraps first N elements from index 0
• ArraySegment:
  • new ArraySegment<T>(array) - Wraps entire array
  • new ArraySegment<T>(array, offset, count) - Wraps segment at any offset

Segmentation Capabilities

• ArrayString: Always starts from index 0, can only specify length
• ArraySegment: Can start from any offset with any count

🔄 Behavioral Similarities

Interface Implementation

Both implement IList<T>, ICollection<T>, IEnumerable<T> with read-only behavior:

• Indexer access (get/set) ✅
• Enumeration support ✅
• Modification operations throw NotSupportedException ✅

Memory Efficiency

Both provide zero-copy views over existing arrays without data duplication.

⚖️ Key Differences

Equality & Hashing

• ArrayString: Content-based equality using EqualTo() extension method
• ArraySegment: Reference-based equality (same array + same offset/count)

Memory Allocation

• ArrayString: Can create new arrays or wrap existing ones
• ArraySegment: Only wraps existing arrays (no allocation)

Performance Characteristics

• ArrayString: Heap allocation overhead, GC pressure
• ArraySegment: Stack allocation, value type copying overhead when passed by value

Default Values

• ArrayString: default is null
• ArraySegment: default is empty segment with Array = null

🧪 Implementation Details

The comparison is implemented as a comprehensive test suite in ArrayStringVsArraySegmentComparisonTests.cs covering:

• Constructor variations and limitations
• Type system differences (class vs struct)
• Interface implementations and capabilities
• Read-only behavior enforcement
• Indexer and enumeration functionality
• Segmentation patterns and constraints
• Equality and hash code generation
• Memory allocation patterns
• Default value handling
• Performance characteristics documentation

📊 Usage Recommendations

Choose ArrayString when:

• You need content-based equality semantics
• You want to create new arrays with specific lengths
• You always work with segments from index 0
• You prefer reference type semantics

Choose ArraySegment when:

• You need arbitrary offset-based segments
• You want minimal allocation overhead
• You prefer value type semantics
• You need .NET BCL consistency

✅ Testing

All comparison tests pass, demonstrating the documented behavior differences and similarities between the two types.

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