mirror of
https://github.com/mruby/mruby
synced 2026-06-08 16:11:16 +00:00
Hiroshi Mimaki
209 lines
3.8 KiB
Markdown
209 lines
3.8 KiB
Markdown
# Limitations and Differences
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The philosophy of mruby is to be a lightweight implementation of
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the Ruby ISO standard. These two objectives are partially contradicting.
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Ruby is an expressive language with complex implementation details which
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are difficult to implement in a lightweight manner. To cope with this,
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limitations to the "Ruby Compatibility" are defined.
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This document is collecting these limitations.
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## Integrity
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This document does not contain a complete list of limitations.
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Please help to improve it by submitting your findings.
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## ```1/2``` gives ```0.5```
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Since mruby does not have ```Bignum```, bigger integers are represented
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by ```Float``` numbers. To enhance interoperability between ```Fixnum```
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and ```Float```, mruby provides ```Float#upto``` and other iterating
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methods for the ```Float``` class. As a side effect, ```1/2``` gives ```0.5```
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not ```0```.
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## ```Array``` passed to ```puts```
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Passing an Array to ```puts``` results in different output.
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```ruby
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puts [1,2,3]
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```
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#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
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```
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1
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2
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3
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```
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#### mruby [1.3.0 (2017-7-4)]
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```
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[1, 2, 3]
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```
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## ```Kernel.raise``` in rescue clause
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```Kernel.raise``` without arguments does not raise the current exception within
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a rescue clause.
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```ruby
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begin
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1 / 0
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rescue
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raise
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end
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```
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#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
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```ZeroDivisionError``` is raised.
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#### mruby [1.3.0 (2017-7-4)]
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No exception is raised.
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## Check of infinite recursion
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mruby does not check infinite recursion across C extensions.
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```ruby
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def test; eval 'test'; end; test
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```
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#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
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```SystemStackError``` is raised.
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#### mruby [1.3.0 (2017-7-4)]
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Segmentation fault.
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## Fiber execution can't cross C function boundary
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mruby's ```Fiber``` is implemented in a similar way to Lua's co-routine. This
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results in the consequence that you can't switch context within C functions.
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Only exception is ```mrb_fiber_yield``` at return.
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## ```Array``` does not support instance variables
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To reduce memory consumption ```Array``` does not support instance variables.
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```ruby
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class Liste < Array
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def initialize(str = nil)
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@feld = str
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end
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end
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p Liste.new "foobar"
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```
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#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
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``` [] ```
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#### mruby [1.3.0 (2017-7-4)]
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```ArgumentError``` is raised.
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## Method visibility
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For simplicity reasons no method visibility (public/private/protected) is
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supported.
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```ruby
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class VisibleTest
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def public_method; end
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private
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def private_method; end
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end
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p VisibleTest.new.respond_to?(:private_method, false)
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p VisibleTest.new.respond_to?(:private_method, true)
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```
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#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
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```
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false
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true
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```
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#### mruby [1.3.0 (2017-7-4)]
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```
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true
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true
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```
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## defined?
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The ```defined?``` keyword is considered too complex to be fully
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implemented. It is recommended to use ```const_defined?``` and
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other reflection methods instead.
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```ruby
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defined?(Foo)
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```
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#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
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```
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nil
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```
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#### mruby [1.3.0 (2017-7-4)]
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```NameError``` is raised.
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## ```alias``` on global variables
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Aliasing a global variable works in CRuby but is not part
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of the ISO standard.
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```ruby
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alias $a $__a__
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```
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#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
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``` nil ```
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#### mruby [1.3.0 (2017-7-4)]
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Syntax error
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## Operator modification
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An operator can't be overwritten by the user.
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```ruby
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class String
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def +
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end
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end
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'a' + 'b'
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```
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#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
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```ArgumentError``` is raised.
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The re-defined ```+``` operator does not accept any arguments.
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#### mruby [1.3.0 (2017-7-4)]
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``` 'ab' ```
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Behavior of the operator wasn't changed.
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## ```Kernel.binding``` missing
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```Kernel.binding``` is not implemented as it is not in the
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ISO standard.
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