mruby-mruby/doc/mruby3.md

User visible changes in mruby3

Build System

build_config directory

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

• host-gprof: compiles with gprof for performance tuning
• host-m32: compiles in gcc 32bit mode on 64bit platforms
• boxing: compiles all three boxing options
• clang-asan: compiles with clang's Address Sanitizer

You can specify the build configration 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

Some configuration macro names are changed for consistency

MRB_NO_FLOAT

Changed from MRB_WITHOUT_FLOAT to conform USE_XXX naming convention.

MRB_USE_FLOAT32

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

Changed from MRB_METHOD_T_STRUCT.

To use struct version of mrb_method_t. More portable but consumes more memory. Turned on by default on 32bit platforms.

MRB_NO_BOXING

Uses struct to represent mrb_value. Consumes more memory but easier to inveticate 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 pointer 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.

Internal Changes

New Instructions

mruby3 introduces a few new instructions.

Instructions that access pool[i]/syms[i] 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

Removed Instructions

Instructions for old exception handling

• OP_ONERR
• OP_POPERR
• OP_EPUSH
• OP_EPOP

No more operand extention

• OP_EXT1
• OP_EXT2
• OP_EXT3

Random now use xoshiro128++.

For better and faster random number generation.