assignment, reference, += and parameter passing

[Pixel <address@hidden>]

Goal: try to see how parameter passing mode interacts with "+="

Interesting difference: python's "+=" handling


(there may be some errors, see my tests examples at
 http://merd.net/pixel/language-study/various/assignment/)
--------------------------------------------------------------------------------
Given:
  def assign(a,b): a = b

after calling "assign(a, b)" is "a" modified?
(where the type of "a" and "b" is one of { Int, String, List })


simple python example:
  a = 0
  assign(a, 1)
  print a
  #=> a is still 0, so answer is "N" 

I S L (where I=Int S=String L=List)
------------------------
N N N Ruby
N N N Python
N N N Java
N N N C++
Y Y Y C++ ref
Y Y Y merd
Y Y _ Perl ref
------------------------
(Y => Yes, N => No)


Given:  
  def add(a,b): a += b

after calling "add(a, b)" is "a" modified?

I S L (where I=Int S=String L=List)
------------------------
N N N Ruby (+=)
_ Y Y Ruby (<<)
N N Y Python (+=)
N N Y Java (+= += addAll)
N N N C++
Y Y Y C++ ref
Y Y Y merd
Y Y _ Perl ref
------------------------


Ruby
  pass-by-ref except for numbers
  "a = b"  "a" is a new object
  "a += b" "a" is a new object
  "a << b" modify the existing object "a" (!not for numbers)

Python
  pass-by-ref except for numbers and strings
  "a = b"  "a" is a new object
  "a += b" modify the existing object "a" (implies a+=b different from a=a+b)

Java
  pass-by-ref except for numbers
  "a = b"  "a" is a new object
  "a += b" "a" is a new object (only works numbers and strings)

C++
  pass-by-value (depth 1), with pass-by-ref possible (using "&")
  "a = b"  modify the existing object "a"
  "a += b" modify the existing object "a" (was not available on vector's)

merd
  pass-by-value (deep) unless as a modified parameter where pass-by-ref is used
  "a = b"  modify the existing object "a"
  "a += b" modify the existing object "a"


Perl
  pass-by-value (depth 1), with pass-by-ref vaguely possible
  "a = b"  modify the existing object "a" (but "a" can't be shared (?))
  "a += b" modify the existing object "a" (but "a" can't be shared (?))
  => no implicit reference so this is not a good test