User visible changes in mruby3.0

Build System

build_config directory

Typical build configuration files are located in build_config directory. For examples:

  • default: the default configuration

  • host-gprof: compiles with gprof for performance tuning

  • host-m32: compiles in gcc 32-bit mode on 64-bit platforms

  • boxing: compiles all three boxing options

  • clang-asan: compiles with clang‘s Address Sanitizer

You can specify the build configuration file with the MRUBY_CONFIG environment variable (or CONFIG in short). If the value specified by MRUBY_CONFIG is not the path to the configuration file, build_config/${MRUBY_CONFIG}.rb is used. So you can specify it as rake MRUBY_CONFIG=boxing, for example.

Build Configuration Contribution

When you write a new build configuration description, please contribute. We welcome your contribution as a GitHub pull-request.

Language Changes

New Syntax

We have ported some new syntax from CRuby.

  • Single line pattern matching (12 => x); mruby matches only with local variables at the moment

  • Numbered block parameter (x.map{_1 * 2})

  • End-less def (def double(x) = x*2)

Configuration Options Changed

Renamed for consistency

Some configuration macro names are changed for consistency (use MRB_USE_XXX or MRB_NO_XXX).

mruby2 mruby3
‘MRB_ENABLE_ALL_SYMBOLS` ‘MRB_USE_ALL_SYMBOLS`
‘MRB_ENABLE_CXX_ABI` ‘MRB_USE_CXX_ABI`
‘MRB_ENABLE_CXX_EXCEPTION` ‘MRB_USE_CXX_EXCEPTION`
‘MRB_ENABLE_DEBUG_HOOK` ‘MRB_USE_DEBUG_HOOK`
‘MRB_DISABLE_DIRECT_THREADING` ‘MRB_NO_DIRECT_THREADING`
‘MRB_DISABLE_STDIO` ‘MRB_NO_STDIO`
‘MRB_METHOD_T_STRUCT` ‘MRB_USE_METHOD_T_STRUCT`
‘MRB_USE_FLOAT` ‘MRB_USE_FLOAT32`
‘MRB_WITHOUT_FLOAT` ‘MRB_NO_FLOAT`
‘ENABLE_LINENOISE` ‘MRB_USE_LINENOISE`
‘ENABLE_READLINE` ‘MRB_USE_READLINE`
‘DISABLE_MIRB_UNDERSCORE` ‘MRB_NO_MIRB_UNDERSCORE`

  • MRB_USE_FLOAT32 is changed from MRB_USE_FLOAT to make sure float here means using single-precision float, and not the opposite of MRB_NO_FLOAT.

  • MRB_USE_METHOD_T_STRUCT uses struct version of mrb_method_t. More portable but consumes more memory. Turned on by default on 32-bit platforms.

  • MRB_ prefix is added to those without.

MRB_NO_BOXING

Uses struct to represent mrb_value. Consumes more memory but easier to investigate the internal and to debug. It used to be default mrb_value representation. Now the default is MRB_WORD_BOXING.

MRB_WORD_BOXING

Pack mrb_value in an intptr_t integer. Consumes less memory compared to MRB_NO_BOXING especially on 32-bit platforms. Fixnum size is 31 bits so some integer values does not fit in Fixnum integers.

MRB_NAN_BOXING

Pack mrb_value in a floating-point number. Nothing changed from previous versions.

MRB_USE_MALLOC_TRIM

Call malloc_trim(0) from mrb_full_gc() if this macro is defined. If you are using glibc malloc, this macro could reduce memory consumption.

Command Line Program

bin/mruby (by mrbgems/mruby-bin-mruby)

The mruby3 now automatically detects *.mrb files without the -b switch. Therefore, it can be mixed with the *.rb file in combination with the -r switch and specified at the same time. Here’s an example that works fine:

$ bin/mruby app.mrb
$ bin/mruby -r lib1.mrb -r lib2.rb app.rb
$ bin/mruby -r lib1.rb -r lib2.rb < app.mrb

Internal Changes

New Instructions

mruby3 introduces a few new instructions.

Instructions that access pool/syms where i>255.

  • OP_LOADL16

  • OP_STRING16

  • OP_LOADSYM16

Instructions that load a 32-bit integer.

  • OP_LOADI32

Instruction that unwinds jump table for rescue/ensure.

  • OP_JMPUW

Renamed from OP_RAISE

  • OP_RAISEIF

Instruction that is reserved for the future keyword argument support.

  • OP_SENDVK

Removed Instructions

Instructions for old exception handling

  • OP_ONERR

  • OP_POPERR

  • OP_EPUSH

  • OP_EPOP

No more operand extension

  • OP_EXT1

  • OP_EXT2

  • OP_EXT3

Changed Instructions

Jump addresses used to be specified by absolute offset from the start of iseq. Now they are relative offset from the address of the next instruction.

Random now use xoshiro128++.

For better and faster random number generation.

Preallocated Symbol

Preallocated symbols are interned at compile-time. They can be accessed via symbols macros (e.g. MRB_SYM()).

See Symbols.