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AGENTS.md

This file provides guidance to LLMs when working with code in this repository.

Project Overview

MemoryViews.jl provides MemoryView, a low-level view into Memory{T} for Julia ≥ 1.11. It's a DenseVector{T} subtype representing a MemoryRef{T} + length, with static mutability tracking via type parameter (Mutable/Immutable). The package also defines the MemoryKind trait for dispatch on memory-backed types.

Commands

# Run tests
JULIA_TEST_FAILFAST=true julia --startup=no --project -e 'using Pkg; Pkg.test()'

# Format code
runic -i .

When running in test mode, Julia has boundscheck always enabled. When running normally, out-of-bounds access in functions marked @inbounds is undefined behaviour. Set --check-bounds=yes to force boundschecking when running experiments.

Architecture

Core types (defined in src/MemoryViews.jl):

  • MemoryView{T, M} where M ∈ {Mutable, Immutable} — the main type
  • MemoryKind trait: IsMemory{T} / NotMemory for dispatch

Source files:

  • construction.jl — constructors from Array, Memory, String, SubArray, CodeUnits
  • basic.jl — indexing, slicing (returns views, not copies), copying, find operations with memchr/memrchr C calls, comparison via memcmp
  • delimited.jl — split_each delimiter iterator
  • base_arrays.jl — Vector/Memory conversion, append
  • io.jl — readbytes!

Extensions (ext/): StringViews, FixedSizeArrays, LibDeflate integration.

Key Patterns

  • Slicing creates views into the same memory (no allocation)
  • Performance-critical paths use @ccall to libc (memset, memcmp, memchr, memrchr) with GC.@preserve
  • Version-conditional code for Julia 1.12+ vs 1.13+ (e.g., Base.memoryindex for parentindices)
  • Trait-based dispatch pattern: define foo(x) → foo(MemoryKind(typeof(x)), x) → specialized on IsMemory/NotMemory
  • @boundscheck/@inbounds used throughout for safe-by-default with opt-in elision