"NOTE:" are changes to be aware of.

mruby now supports pattern matching (case/in) syntax:

• Basic pattern matching with case/in syntax (dadfac6)
• Array pattern matching (ec67fd9)
• Hash pattern matching (2147263)
• Find pattern matching ([*pre, target, *post]) (6c4d98b)
• Pin operator (^variable) (1de6340)
• Guard clauses (if/unless conditions) (07ac110)
• One-line pattern matching (expr in pattern) (e76ce24)
• Brace-less hash pattern support (e8096bf)

• Array/Hash/String subclasses can now override [] and []= methods (#6675)
• OP_SETIDX optimization for Array and Hash (ddd8fe1)

• NOTE: mruby/ext/io.h renamed to mruby/io.h (2813f79)
• mrb_time_get_tm() API for accessing struct tm (daaaafe)
• MRB_OPEN_FAILURE() macro for checking mrb_open result (40b0cb9)
• mrb_print_error() now handles NULL gracefully (8e50a45)
• mrb_open() returns mrb_state with exc set on init failure (05ffe0c)
• mrb_utf8_to_buf() for UTF-8 encoding consolidation (7e28e68)
• kh_is_end() macro for safe khash iteration (893cc75)

• New Platform: Cosmopolitan Libc (#6681)
• Emscripten: use native WASM exception handling (ca364e3)
• HAL (Hardware Abstraction Layer) for platform abstraction in mruby-io, mruby-socket, mruby-dir, mruby-task (74ca22f)
• MRUBY_MIRB_READLINE environment variable to control readline library selection (0aafb83)
• Inter-gem headers separated from external API headers (#6671)

• mruby-task: Cooperative multitasking with preemptive scheduling (ae0d7a0)
• mruby-benchmark: Benchmarking gem (2f40f3d)
• mruby-strftime: Time#strftime implementation (b31e22f)

• Custom multi-line editor replacing readline (527018c)
• Tab completion support (2f15282)
• Colored output for prompts and errors (b36e0b4)
• Auto-indentation for continuation lines (d52f318)
• TAB auto-indentation (fa74186)
• Auto-dedent for else, elsif, when, rescue, ensure, in (e901b6d, 814b0cc)
• Command history with Up/Down navigation (5f85c1b)
• Line numbers in multi-line prompts (5a3f0e2)
• Enhanced syntax error display (ac39b7d)

• mruby-array-ext: Add Array#find and Array#rfind methods
• mruby-io: Add IO#putc and Kernel#putc (baff6e6)
• mruby-random: Replace xoshiro with PCG for better memory efficiency (f1bab01)
• mruby-compiler: Variable-sized AST nodes for reduced memory usage
• mruby-compiler: no_return_value context flag for script optimization (613b03a)

• Variable-sized AST nodes for reduced memory consumption (821b989)
• Pattern matching bytecode optimizations (21d4135)
• Optimized masgn to generate literals directly into target registers (fb5d966)
• Optimized splat of literal arrays in args/literals (1cb8d73)

New super-instructions that fuse common opcode sequences to reduce bytecode size and improve performance:

• OP_TDEF/OP_SDEF: Fused method definition combining TCLASS/SCLASS+METHOD+DEF into single instruction, saving 4 bytes per method (8d4f47e)
• OP_GETIDX0: Fast path for array[0] and Array#first access (680f7ec)
• OP_ADDILV/OP_SUBILV: Local variable increment/decrement fusion for i += n patterns (43f64b9)
• OP_RETSELF: Single-byte instruction for return self pattern (a71db8c)
• OP_MATCHERR: Pattern matching error with conditional execution for in patterns (944168a, e9a9ba4)
• OP_BLKCALL: Direct block call for yield, bypassing method dispatch (13-17% faster) (3aa2872)
• OP_RETNIL: Single-byte instruction for return nil pattern (64e30bf)
• OP_RETTRUE/OP_RETFALSE: Single-byte instructions for return true/return false patterns (0b15727)

• #6675 Allow Hash#[] to be aliased again
• #6674 Document pattern matching limitations
• #6671 Separate inter-gem headers from external API headers
• #6668 Method#== for aliased methods and comparison bug
• #6666 Regexp literal with encoding
• #6664 Set#flatten memory leak
• #6662 Array set operations use-after-free
• #6660 Regression on struct/array/hash == override with super
• #6659 Super with keyword arguments
• #6657 Exception handling for ||= on class variables
• #6652 Array comparison use-after-realloc
• #6650 Array#fill validation
• #6649 Array#sort! use-after-realloc
• #6648 sprintf buffer overread
• #6647 IO#ungetc buffer overflow
• #6646 IO#gets negative length
• #6645 Set memory leak from double initialization
• #6642 Task segfault when sleep called from C
• #6637 arm64 mingw64 builtin setjmp/longjmp
• #6635, #6636 Colon3 constant lookup
• #6613 const_added hook during bootstrapping
• #6570 instance_eval crash
• #6554 Socket private #initialize
• #6516 Private backquote
• #6515 y.tab.c in repository
• #6509 scope_new nregs initialization
• #6508 Enumerable#sum index
• #6507 tally multi-values
• #6506 Constant lookup in singleton class
• #5531 Hash recursion detection

• #6418 Add ls-lint with GitHub Actions
• #6492 fix a typo, update specs
• #6493 Fix TYPO in memory.md
• #6495 Remove MRB_ENDIAN_LOHI() that is no longer in use
• #6497 gha: update build.yml try windows-2025 image
• #6498 Clean up and standardize the pre-commit config
• #6501 Update pre-commit Node.js version to v22.14.0 LTS
• #6502 pre-commit: update prettier to the latest version
• #6503 misc: fix typos
• #6505 mrbgems: fix spelling
• #6510 Fixed class method visibility via module_function
• #6511 Exclude the external project "lrama" from pre-commit
• #6513 mruby 3.4.0 released
• #6517 core/codegen.c: remove unneeded duplicate semicolon
• #6518 Change mrbc_args.flags bit width from 2 to 3
• #6519 Add tools/lrama to .prettierignore
• #6520 pre-commit: autoupdate and update node LTS version
• #6521 Add codespell config file .codespellrc
• #6522 gha: label more files
• #6523 add rand(Range) and unify implementations of Random#rand and Kernel#rand
• #6524 Fix Kernel#p when no argument
• #6525 Skip adding empty input to mirb history
• #6526 Add build config for Luckfox Pico embedded SBC
• #6528 misc: fix spelling
• #6530 Revert "class.c (find_visibility_scope): when callinfo returns, *ep == NULL; #6512"
• #6531 Improve method table performance by rehashing at 75% load factor
• #6532 Reverted method table optimizations to prioritize memory savings
• #6533 Fix calling extended callback
• #6534 Add descriptive comment to mrb_read_float function
• #6535 Added descriptive comments for functions/macros in src/mempool.c
• #6536 Add descriptive comments to public functions in src/debug.c
• #6537 Updated comments in cdump.c to remove the @brief tag
• #6539 Add descriptive comments for functions in src/load.c
• #6540 Add descriptive comments to MRB_API functions in object.c
• #6541 Add descriptive comments for MRB_API functions in src/array.c
• #6542 Add descriptive comments to MRB_API functions in src/symbol.c
• #6543 Add descriptive comments to several functions in src/dump.c
• #6544 Fix build strings that must be mutable
• #6545 Add descriptive comments for MRB_API functions in src/class.c
• #6548 Add descriptive comments to MRB_API functions in src/etc.c
• #6549 Add descriptive comments to kernel functions
• #6550 Add descriptive comments for MRB_API functions in src/proc.c
• #6551 Add descriptive comments for MRB_API functions in src/state.c
• #6552 Fix: Correct placement of comments in src/variable.c
• #6553 Add descriptive comments for MRB_API functions in src/vm.c
• #6555 mrb_mt_foreach() needs to update the pointer at each loop
• #6556 iv_foreach() needs to update the pointer at each loop
• #6560 Refactor: Improve Set GC marking and freeing
• #6561 pre-commit updates and fix prettier entrypoint
• #6562 misc: fix spelling word case
• #6563 pre-commit add rubocop with one rule spaces for indentation
• #6564 Remove jumanjihouse pre-commit hooks no longer maintained
• #6565 Rubocop: fix target Ruby version; add two more cops; fix lint error
• #6566 Removed unreferenced variables in CrossBuild#run_bintest
• #6567 Avoid array object creation in cmd_bin method in bintest
• #6568 mruby-bin-debugger depends on mruby-bin-mrbc in bintest
• #6569 sed s/Mruby/MRuby/g
• #6571 Update limitations.md to add behavior on small hash
• #6572 Add Claude Code GitHub Workflow
• #6573 pre-commit fixes and updates
• #6574 Support initializing structs via keyword arguments
• #6575 Fix typo in file time methods
• #6581 Merge mrb_obj_iv_inspect() into mrb_obj_inspect()
• #6582 Stricter type tag in mrb_obj_alloc()
• #6583 Add fallback to local build_config.rb before using default configuration
• #6585 Fix typo in mruby3.2 docs
• #6586 Makefile: refactor add docs and add command line help target
• #6587 Add Set#hash tests
• #6588 Add CodeQL Analysis for GitHub Actions
• #6589 Add pre-commit hook check-zip-file-is-not-committed
• #6591 mruby-eval fix license link in README
• #6593 README: Add Contributors Avatars, Star History, Table of Contents
• #6599 pre-commit: run markdown-link-check, oxipng, prettier manually
• #6600 dreamcast_shelf build config: update to use KallistiOS wrappers
• #6601 fix: skip local build_config.rb when working in MRUBY_ROOT
• #6602 Improved iseq annotations for new and !=
• #6604 pre-commit config updates
• #6607 fix bigint on raspberry pi
• #6610 Extract golden ratio prime into constant
• #6614 Fix uninitialized variable in io_gets causing segmentation fault
• #6617 Fix various minor problems and speed up build
• #6618 Stop generating unnecessary C++ files in mruby-bin-mruby
• #6621 Set up all GEMS before mruby core tasks definition
• #6624 Fixed wrong MRuby::Build.current at the top level of mrbgem.rake
• #6628 Revert File.absolute_path logic
• #6629 pre-commit update
• #6631 Revert "Rakefile: make the whole thing parallel unless SERIAL=1"
• #6633 Fix a heap-buffer-overflow in str strip! methods
• #6643 Fix crash caused by an incorrect node type check in codegen_masgn
• #6651 Address stack-use-after-return in the mruby bigint implementation
• #6653 Improve HAL-related components for MinGW
• #6655 Preventing Memory Leaks in Array#__combination_init
• #6656 Fix integer overflow in allocation size calculation
• #6663 Added the kh_is_end() macro function
• #6665 Fixed use-after-free with Set#join
• #6670 Arranging VM dispatch macros
• #6673 Adjust broken license links; clean up Markdown
• #6677 gha: run pre-commit with --color=always
• #6678 Put ls-lint and pre-commit in separate workflow files
• #6679 pre-commit autoupdate; update node and prettier
• #6681 Add Cosmopolitan Libc build configuration

• Buffer overflow in bigint uadd (3f2611e)
• Buffer overflow in pack_uu encoding (2993302)
• Buffer overflow in IO#ungetc (01ab2ff)
• Use-after-free in Set operations (a6b55e7)
• Use-after-free in Array set operations (729b84c)
• Use-after-free in Set#join (0e653eb)
• Use-after-realloc in Array#sort! (eb39897)
• Multiple memory leak fixes in bigint, Set, Array, and Task gems