mruby-mruby/doc/mruby3.md

User visible changes in mruby3 from mruby2 (as of mruby3.1)

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 32bit mode on 64bit 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 32bit 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. Inlined integer size is 31 bits, so some mrb_int values does not fit in mrb_value. Those integers are allocated in the object heap as struct RInteger.

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.

OP_LOADI16 and OP_LOADI32

Load a 16/32-bit integer.

OP_JMPUW

Unwinds jump table for rescue/ensure.

OP_RAISEIF

Renamed from OP_RAISE

OP_SYMBOL

Generates a symbol from the pool string. This is a combination of OP_STRING and OP_INTERN.

OP_GETIDX and OP_SETIDX

Execute obj[int] and obj[int] = value respectively, where obj is string|array|hash.

OP_SSEND and OP_SSENDB

They are similar to OP_SEND and OP_SENDB respectively. They initialize the R[a] by self so that we can skip one OP_LOADSEND instruction for each call.

Changed Instructions

Jump 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.

OP_SEND and OP_SENDB

Method calling instructions are unified. Now OP_SEND and OP_SENDB (method call with a block) can support both splat arguments and keyword arguments as well.

The brief description of the instructions:

|OP_SEND | BBB | R(a) = call(R(a),Syms(b),R(a+1..n),R(a+n+1),R(a+n+2)..nk) c=n|nk<<4 | |OP_SENDB | BBB | R(a) = call(R(a),Syms(b),R(a+1..n),R(a+n+1..nk),R(a+n+2..nk),&R(a+n+2*nk+2)) c=n|nk<<4 |

When n == 15, the method takes arguments packed in an array. When nk == 15, the method takes keyword arguments packed in a hash.

OP_ARYPUSH

Now takes 2 operands and pushes multiple entries to an array.

Removed Instructions

Instructions for old exception handling

• OP_ONERR
• OP_POPERR
• OP_EPUSH
• OP_EPOP

Instructions for method calls with variable number of arguments. They are covered by OP_SEND instruction with n=15.

• OP_SENDV
• OP_SENDVB

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.