Because literal pool may be released by GC.
#### Example:
```ruby
s1 = eval('"abcdefghijklmnopqrstuvwxyz01"')
GC.start
p s1 #=> "\x00\x00\x00\x00\x00\x00\x00\x90\x00\x00\x00\x00\x00\x00\x00\x90\x03\x00stuvwxyz01"
```
#### Example (with `MRB_METHOD_CACHE`)
```ruby
GC.start
c = Class.new
p c #=> #<Class:0x7fd6a180e790>
c.new #=> cache `c.new`
c = nil
GC.start #=> `c` is GCed
r = Range.dup
p r #=> #<Class:0x7fd6a180e790>
# [same pointer as `c`]
r.new(2, 3) #=> ArgumentError: 'initialize':
# wrong number of arguments (2 for 0)
# [`c.new` is called instead of `r.new`]
```
#### Cause
An entry of method cache is identified by class pointer and method
id. However, reusing memory after GC may create a class with the same
pointer as the cached class.
#### Treatment
Cleared method caches of the class when the class is GCed.
The following improvements are made according to Ruby's behavior:
- Match location number to index.
- Remove duplicate most recent call output.
- Fix that first call is not output when array (unpacked) backtrace.
### Example
```ruby
def a; raise "error!" end
def b; a end
begin
b
rescue => e
e.backtrace if ARGV[0] == "unpack" # unpack backtrace
raise e
end
```
#### Before this patch:
```
$ bin/mruby example.rb unpack
trace (most recent call last):
[0] example.rb:2:in b
[1] example.rb:1:in a
example.rb:1: error! (RuntimeError)
```
#### After this patch:
```
$ bin/mruby example.rb unpack
trace (most recent call last):
[2] example.rb:4
[1] example.rb:2:in b
example.rb:1:in a: error! (RuntimeError)
```
Because location info (file name and line number) is kept in the backtrace,
it should not be kept in the result of `inspect` (and the exception object
itself), I think.
### Example
```ruby
# example.rb
begin
raise "err"
rescue => e
p e
end
```
#### Before this patch:
```
$ bin/mruby example.rb
example.rb:2: err (RuntimeError)
```
#### After this patch:
```
$ bin/mruby example.rb
err (RuntimeError)
```
#### Before this patch:
```
$ mruby -e '[].each(1){}' #=> no error
```
#### After this patch:
```
$ mruby -e '[].each(1){}' #=> ArgumentError: wrong number of arguments
```
Consecutive `_` is not allowed as a numeric expression:
1_2__3 #=> SyntaxError
Float("1_2__3") #=> ArgumentError
Integer("1_2__3") #=> ArgumentError
"1_2__3".to_i #=> 12
But `String#to_f` accept it, so I fixed the issue.
Before this patch:
"1_2__3".to_f #=> 123
After this patch:
"1_2__3".to_f #=> 12
If ":" is after "|" and there is no "?" or "*", the keyword argument
could not be obtained and it was not initialized with `undef`.
For example: "|oo:"
* The allocated memory is guaranteed to be aligned for any data type (it was
not guaranteed when string type is embed).
* Make allocation size exactly specified size (does not allocate space for a
null byte).
Previously, `mrb_int` was used as the type that represents the buffer size
on memory, but the sizes of `RString` and `RArray` exceed 6 words when
`MRB_INT64` is enabled on 32-bit CPU.
I don't think it is necessary to be able to represent the buffer size on
memory that exceeds the virtual address space. Therefore, for this purpose,
introduce `mrb_ssize` which doesn't exceed the sizes of `mrb_int` and
pointer.
I think all `mrb_int` used for this purpose should be changed to
`mrb_ssize`, but currently only the members of the structures (`RString`,
`mrb_shared_string`, `RArray` and `mrb_shared_array`) are changed.
### Benchmark (with `MRB_UTF8_STRING`)
```
$ mruby -e '
COUNT = 150000
SIZE = 10000
strs = Array.new(COUNT) do
s = "a" * SIZE
s.size # set `MRB_STR_ASCII` flag
s
end
i = 0
t = Time.now
while i < COUNT
strs[i][-2..-1] = ""
i += 1
end
printf "%.2f sec\n", Time.now - t
'
1.10 sec # before
0.07 sec # after
```
### Benchmark (with `MRB_UTF8_STRING`)
```ruby
# benchmark.rb
COUNT = 300000
SIZE = 10000
s = "a" * SIZE
s.size # set `MRB_STR_ASCII` flag
i = 0
while i < COUNT
s[-1]
i += 1
end
```
#### Before this patch:
```
$ time mruby benchmark.rb
2.06 real 2.05 user 0.00 sys
```
#### After this patch:
```
$ time mruby benchmark.rb
0.05 real 0.04 user 0.00 sys
```
### Example (with `MRB_UTF8_STRING`)
```ruby
s = "\u3042"
p s.size
s.dump
p s.size
```
#### Before this patch:
```
1
3
```
#### After this patch:
```
1
1
```
Yukihiro "Matz" Matsumoto