mruby 2.1.0

We are proudly announcing the stable release of mruby 2.0 series - mruby 2.1.0.
The mruby 2.1.0 has been enhanced with compatibility with Ruby 2 series, and some new features of Ruby 2.7 have been added.

New Features

Core Language Features

  • Suffix support (Rational and Complex literals) (#4125)

Core Libraries

Ruby 2.7 features

  • Add Array#intersection method which returns a new array containing elements common to both arrays. (mrbgems/mruby-array-ext)
  • Add Enumerable#filter_map method which is a short hand for filter + map in a single call. (mrbgems/mruby-enum-ext)
  • Add Enumerable#tally method which group and count elements of the collection. (mrbgems/mruby-enum-ext)
  • Add Enumerator.produce method which creates an infinite enumerator from any block. (mrbgems/mruby-enumerator)
  • Add UnboundMethod#bind_call method which call a method that overridden without allocation of intermediate Method object. (mruby-method)
  • Module#name, true#to_s, false#to_s return a frozen string. The returned string is always the same object.

Ruby 2.6 features

  • Add Array#difference method:
    Array#difference returns a new array that is a copy of the original array, removing any items that also appear in other_ary. (mrbgems/mruby-array-ext)

New Libraries

  • Add mrbgems/mruby-rational:
    Rational class has been included into the core library, and rational numbers like 1/3 can be handled.
  • Add mrbgems/mruby-complex:
    Complex class has been included into the core library to handle complex numbers.

New C APIs

Macros for checking object type


mruby core (mruby.h)

MRB_API mrb_int mrb_cmp(mrb_state *mrb, mrb_value obj1, mrb_value obj2);

mruby binary (mruby/dump.h, mruby/irep.h)

MRB_API mrb_irep *mrb_read_irep_buf(mrb_state*, const void*, size_t);   // mruby/dump.h
MRB_API mrb_value mrb_load_irep_buf(mrb_state*, const void*, size_t);   // mruby/irep.h
MRB_API mrb_value mrb_load_irep_buf_cxt(mrb_state*, const void*, size_t, mrbc_context*);   // mruby/irep.h

Numeric class (mruby/numeric.h)

MRB_API mrb_value mrb_num_plus(mrb_state *mrb, mrb_value x, mrb_value y);
MRB_API mrb_value mrb_num_minus(mrb_state *mrb, mrb_value x, mrb_value y);
MRB_API mrb_value mrb_num_mul(mrb_state *mrb, mrb_value x, mrb_value y);
MRB_API mrb_value mrb_int_value(mrb_state *mrb, mrb_float f);

String class (mruby/string.h)

MRB_API void mrb_str_modify_keep_ascii(mrb_state *mrb, struct RString *s);
MRB_API const char *mrb_string_cstr(mrb_state *mrb, mrb_value str);


  • Add customized mrb_ro_data_p() (#4408)

Enumerable module and Hash class

  • Add filter aliases for Enumerable and Hash. (57a0132b)


  • (Proof of Concept) mruby tuning profiles (#4446)


Test Features

  • Warn if assertion is missing inside assert (#4320)

New test method (mrbtest)

assert_match(pattern, str, msg=nil)
assert_not_match(pattern, str, msg=nil)
assert_raise_with_message(exc, exp_msg, msg = nil, &block
assert_raise_with_message_pattern(exc, exp_msg, msg = nil, &block)
assert_not_nil(target, msg)


Interactive mruby (mirb)

  • As with irb in Ruby, a local variable _ is added to store the last result.

Update Features

mruby core

  • Allow newlines and comments between method calls. (4296c77e)
  • Support &. at the beginning of the line (4124047c)

Build system

  • Support lock file
    It is now possible to fix mruby and mrbgems versions in products that use mruby.
  • Rename MRB_USE_ETEXT_EDATA to MRB_USE_LINK_TIME_RO_DATA_P and support lld linked programs (#4716)


mruby core

  • Keyword arguments can be obtained with mrb_get_args using the format string :.
  • mrb_parser_dump supports displaying NODE_DSYM, NODE_WORDS, NODE_SYMBOLS and NODE_LITERAL_DELIM.
  • Raise ArgumentError by aspec check. (30f37872)


  • Add new specifiers/modifiers to format string of mrb_vfromat() (#4608)


  • Nested assert for mrbtest (#4540)


mruby core

  • Pad leading zero to month and day in MRUBY_RELEASE_DATE (#4353)

Core Libraries

  • Add Class#new(*args, &block) method.
  • Add optional argument to Module#class_variables.
  • Add constants for floating point number. (RADIX, MANT_DIG, EPSILON, DIG, MIN_EXP, MIN, MIN_10_EXP, MAX_EXP, MAX, MAX_10_EXP)
  • Removed $1..$9 from Kernel#global_variables.
  • String#unpack/Array#pack does support base64 directive (m).
  • Add encoding argument to Integral#chr (#4593)
  • Fixed length for IO should be in bytes, not in characters (8c90b5fc)

Breaking Changes

There are three major breaking changes from mruby 2.0.1.

Changed methods

  • Move Array#append and Array#prepend from core to mrbgems/mruby-ary-ext.
  • Move Numeric#div from mrbgems/mruby-numeric-ext to the core.
  • Move Integral#zero?, Integral#nonzero?, Integral#positive? and Integral#negative)? to Numeric class.
  • Move Numeric#__coerce_step_counter to Integral class.
  • Move Kernel#instance_exec, Kernel#equal? and Kernel#instance_eval to BasicObject class.
  • Move NilClass#to_h to mrbgems/mruby-object-ext from mrbgems/mruby-enum-ext
  • Move String#getbyte, String#setbyte and String#byteslice to the core. (#4696)
  • Remove Kernel#global_variables from core. This method is defined in mrbgems/mruby-metaprog.
  • Integrate Integral#chr (Fixnum#chr) to mrbgems/mruby-string-ext.
  • Remove String#=~ and String#match that requires Regexp (fd37bc53)
  • Symbol#to_s return a frozen string. The returned string is always the same object. This feature will be reverted next mruby, because which reverted from Ruby 2.7.
  • Explicit .0 is removed from result of Float#to_s and Float#inspect. (9d08025b)

Change C APIs

  • Rename symbol-to-string functions. (#4684)
    • mrb_sym2name() -> mrb_sym_name()
    • mrb_sym2name_len() -> mrb_sym_name_len()
    • mrb_sym2str() -> mrb_sym_str()

Remove C APIs

  • Functions to remove MRB_API from definitions (referenced from within libmruby):
    mrb_instance_new(), mrb_vm_define_class(), mrb_vm_define_module()
  • struct RIstruct is renamed to struct RIStruct (e41f1574)
  • Remove mrb_fixnum_plus(), mrb_fixnum_minus(), mrb_fixnum_mul(), and mrb_num_div(). Use mrb_num_plus(), mrb_num_minus(), mrb_num_mul() instead.
  • Remove a member ary of struct RString. struct RStringEmbed is used for String embedding. (#4646)

mruby core

  • Remove global variable $/. The current Ruby policy do not encourage Perl-ish global variables.
  • Remove MRB_TT_HAS_BASIC macro. (#4728)
  • Remove members flags and mems of struct mrb_state. (0c5f26e0 and #4470)


  • Remove MRB_METHOD_TABLE_INLINE and MRB_NO_INIT_ARRAY_START. (2256bb07 and #4716)
  • MRB_USE_ETEXT_EDATA is deprecated (warned and ignored). instead, use MRB_USE_LINK_TIME_RO_DATA_P. (#4716)

mruby binary (MRB)

  • Remove “LINE” section reader. (#4455)

Major bug fixes

  • SystemStackError is raised from String#=~. (#4363)
  • Null pointer dereference in ecall. (#4370)
  • mismatched shift functions. (#4380)
  • Compilation error with “MRB_ARY_EMBED_LEN_MAX” in “array.h”. (#4382)
  • Fixed a bug in recursive mrb_top_run calls; fix (#4384)
  • Unexpected error: Can't get cfunc env from non-cfunc proc. (#4389)
  • build error on master by MRB_WITHOUT_FLOAT. (#4478)
  • Null pointer dereference in mrb_str_cat_str. (#4504)
  • Some comments do not increment lineno on context. (#4513)
  • Null pointer dereference in mrb_check_frozen. (#4519)
  • Invalid read in mrb_class. (#4534)
  • Array#inspect recurses too much for self-referential arrays. (#4552)
  • Infinite loop in Integer#step when both args are INFINITY. (#4555)
  • Float#round hangs for large ndigits. (#4566)
  • Cannot call Fiber.yield in method. (#4567)
  • Reference to top-level variable in top-level block is broken. (#4581)
  • Bugs with mutually recursive Array and Hash. (#4582)
  • mrb_gc_unregister() may access freed memory. (#4618)
  • memcpy-param-overlap in str_replace_partial. (#4627)
  • Symbol#inspect does not handle Unicode characters. (#4678)
  • mrb_funcall returns odd value. (#4696)
  • behavior of alias is defferent from CRuby. (#4718)
  • compile error at master by clang 9. (#4786)

We have done 912 commits to 229 files, 12,006 lines were added, 5,382 lines removed since mruby 2.0.1. For more detail of the updates, see Commit Log.

Let’s try mruby 2.1.0.