memory

InlineArray and Span

Guidance for Swift 6.2's low-level memory types: InlineArray for fixed-size inline storage without heap allocation, and Span for safe, zero-cost access to contiguous memory. These replace common uses of UnsafeBufferPointer and hand-tuned tuple storage with compiler-checked alternatives.

When This Skill Activates

Use this skill when the user:

• Asks about InlineArray, fixed-size arrays, or stack-allocated collections
• Mentions Span, MutableSpan, RawSpan, or UTF8Span
• Wants to eliminate heap allocations in hot paths
• Is replacing UnsafeBufferPointer or UnsafePointer with safe alternatives
• Asks about value generics or let count: Int generic parameters
• Needs zero-copy access to collection storage
• Mentions inline storage, contiguous memory, or memory layout
• Is doing binary parsing, signal processing, or embedded Swift work
• Wants to avoid copy-on-write overhead for small fixed collections
• Asks about non-escapable types or lifetime dependencies in Swift

Decision Tree

What memory optimization do you need?
│
├─ A fixed-size collection that never grows/shrinks
│  │
│  ├─ Size known at compile time, stored on stack
│  │  └─ InlineArray<N, Element>
│  │     ├─ No heap allocation
│  │     ├─ No reference counting
│  │     └─ No copy-on-write (eager copies)
│  │
│  └─ Size may vary at runtime
│     └─ Array<Element> (standard library)
│
├─ Safe read access to contiguous memory
│  │
│  ├─ Read-only access to typed elements
│  │  └─ Span<Element>
│  │
│  ├─ Mutable access to typed elements
│  │  └─ MutableSpan<Element>
│  │
│  ├─ Read-only access to raw bytes
│  │  └─ RawSpan
│  │
│  ├─ Mutable access to raw bytes
│  │  └─ MutableRawSpan
│  │
│  ├─ Unicode text processing
│  │  └─ UTF8Span
│  │
│  └─ Initializing a new collection's storage
│     └─ OutputSpan
│
├─ Unsafe pointer access (legacy or interop)
│  └─ UnsafeBufferPointer / UnsafeMutableBufferPointer
│     └─ Prefer Span instead for new code
│
└─ Standard dynamic collection
   └─ Array<Element>
      ├─ Heap-allocated, copy-on-write
      └─ Grows/shrinks dynamically