mruby-mruby/doc/mruby3.md

User visible changes in mruby3

Build System

You can specify TARGET option to rake via a command line option, or via an environment variable, e.g.

rake TARGET=host all

or

TARGET=host rake all

It's much easier to switch multiple targets than the previous build_config.rb system.

presym target

The first compilation of mruby may require generation of a static symbol table named build/presym. You can generate the table by rake gensym.

target directory

Build target specification files are loaded from target directory. The default TARGET is host which is described in target/host.rb. There are many other targets for example:

• 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

target/host.rb comes with comments to help writing a new target description.

If you want to have your target description out of the source tree, you can specify the path to the description file in MRUBY_CONFIG.

Build Target Contribution

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

Language Changes

New Syntax

We have ported some new syntax from CRuby.

• R-assignment (12 => x)
• 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

Random now use xoshiro128++.

For better and faster random number generation.