1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
|
# Limitations and Differences
The philosophy of mruby is to be a lightweight implementation of
the Ruby ISO standard. These two objectives are partially contradicting.
Ruby is an expressive language with complex implementation details which
are difficult to implement in a lightweight manner. To cope with this,
limitations to the "Ruby Compatibility" are defined.
This document is collecting these limitations.
## Integrity
This document does not contain a complete list of limitations.
Please help to improve it by submitting your findings.
## ```1/2``` gives ```0.5```
Since mruby does not have ```Bignum```, bigger integers are represented
by ```Float``` numbers. To enhance interoperability between ```Fixnum```
and ```Float```, mruby provides ```Float#upto``` and other iterating
methods for the ```Float``` class. As a side effect, ```1/2``` gives ```0.5```
not ```0```.
## ```Array``` passed to ```puts```
Passing an Array to ```puts``` results in different output.
```ruby
puts [1,2,3]
```
#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
```
1
2
3
```
#### mruby [1.2.0 (2015-11-17)]
```
[1, 2, 3]
```
## ```Kernel.raise``` in rescue clause
```Kernel.raise``` without arguments does not raise the current exception within
a rescue clause.
```ruby
begin
1 / 0
rescue
raise
end
```
#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
```ZeroDivisionError``` is raised.
#### mruby [1.2.0 (2015-11-17)]
No exception is raised.
## Check of infinite recursion
mruby does not check infinite recursion across C extensions.
```ruby
def test; eval 'test'; end; test
```
#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
```SystemStackError``` is raised.
#### mruby [1.2.0 (2015-11-17)]
Segmentation fault.
## Fiber execution can't cross C function boundary
mruby's ```Fiber``` is implemented in a similar way to Lua's co-routine. This
results in the consequence that you can't switch context within C functions.
Only exception is ```mrb_fiber_yield``` at return.
## ```Array``` does not support instance variables
To reduce memory consumption ```Array``` does not support instance variables.
```ruby
class Liste < Array
def initialize(str = nil)
@feld = str
end
end
p Liste.new "foobar"
```
#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
``` [] ```
#### mruby [1.2.0 (2015-11-17)]
```ArgumentError``` is raised.
## Method visibility
For simplicity reasons no method visibility (public/private/protected) is
supported.
```ruby
class VisibleTest
def public_method; end
private
def private_method; end
end
p VisibleTest.new.respond_to?(:private_method, false)
p VisibleTest.new.respond_to?(:private_method, true)
```
#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
```
false
true
```
#### mruby [1.2.0 (2015-11-17)]
```
true
true
```
## defined?
The ```defined?``` keyword is considered too complex to be fully
implemented. It is recommended to use ```const_defined?``` and
other reflection methods instead.
```ruby
defined?(Foo)
```
#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
```
nil
```
#### mruby [1.2.0 (2015-11-17)]
```NameError``` is raised.
## ```alias``` on global variables
Aliasing a global variable works in CRuby but is not part
of the ISO standard.
```ruby
alias $a $__a__
```
#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
``` nil ```
#### mruby [1.2.0 (2015-11-17)]
Syntax error
## Operator modification
An operator can't be overwritten by the user.
```ruby
class String
def +
end
end
'a' + 'b'
```
#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
```ArgumentError``` is raised.
The re-defined ```+``` operator does not accept any arguments.
#### mruby [1.2.0 (2015-11-17)]
``` 'ab' ```
Behavior of the operator wasn't changed.
## ```Kernel.binding``` missing
```Kernel.binding``` is not implemented as it is not in the
ISO standard.
|
