From: Paul Magnussen <lists@...>
Date: 2012-12-23T08:15:58+09:00
Subject: POLS and string-handling

Hi,

I have programmed in various languages previously, but am new to Ruby.

So far am very impressed with it; but there is one behaviour I find
quite alarming, which stems from the fact that Ruby treats strings as
objects rather than as primitives.

For instance:

# a) Number

myNum1 = 5
myNum2 = myNum1

myNum2 = 3

=> myNum1 = 5
=> myNum2 = 3

which is what I would expect.  However,

# b) String

myString3 = "Fred Nerk"
myString4 = myString3

myString4[0,4] = "Bert"

=> myString3 = "Bert Nerk"
=> myString4 = "Bert Nerk"

myString3 has been "corrupted", presumably because setting myString4 to
it actually set myString4's pointer, not its value, in the standard OO
fashion.

But

# c) String literal

myString1 = "Fred Bloggs"
myString2 = myString1

myString2[0,4] = "Bert"

puts "Fred Bloggs = " + "Fred Bloggs"
puts "myString2 = " + myString2

(Output)

=> Fred Bloggs = Fred Bloggs
=> myString2 = Bert Bloggs

Has the "Fred Bloggs" literal not been corrupted?  Or did puts just use
another (uncorrupted) instance of it?

So let's make the first string a constant.  That produces the expected
behaviour in this case:

# d) String constant 1

MyString5 = "Fred Potts"
MyString5 = "John Potts"

=> warning: already initialized constant MyString5

but not in this one:  the constant gets "corrupted".

# e) String constant 2

MyString6 = "Fred Winterbotham"
myString7 = MyString6

myString7[0,4] = "Bert"

=> MyString6 = "Bert Winterbotham"
=> myString7 = "Bert Winterbotham"

So how to get around this?  The following appears to do it:

# f) String constant 3

MyString8 = "Fred Shufflebotham"
myString9 = MyString8.clone

myString9[0,4] = "Bert"

=> MyString8 = "Fred Shufflebotham"
=> myString9 = "Bert Shufflebotham"

but doesn't it cause a memory leak?

Sorry if this question is too elementary.

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