Programming language inventor OR serial killer?

Kóder vagy sorozatgyilkos?

Can you tell a coder from a cannibal? Try to work out which of the following spent their time hacking computers and which preferred hacking away at corpses instead.

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The bad and ugly: Ruby strings

Ruby is a language like Java, everything is reference to object. An assignment does not produce copy of the value, but the copy of the reference. So if you have an a object, and you say b=a then you will have a b object reference pointing to the same place as a.

The naive approach of a string is that if I say a='x12345y'; b=a; b.sub!('234','---'); will result in an a which's value is 'x12345y' and a b which's value is 'x1---5y'.

The Java guys invented the immutable pattern which means that after a string is created it cannot be modified. The sensation of modification comes from the construction of new strings from old ones, like s = s.concat("TEST") where s.concat("TEST") creates a new string which's reference may or may not be stored back at s itself.

But Ruby has weird behavior:

original = '|123|123|123|123|'
s = original
s['123']='TEST'
print(s,"\n")
s = original
s.sub!('123','TEST')
print(s,"\n")

will output

|TEST|123|123|123|
|TEST|TEST|123|123|

You do not know enough - they say, There are immutable objects in ruby too!. I just have to call the freeze method and the object will be immutable. Let's try it.

original = '|123|123|123|123|'
original.freeze # <--- NEW GUY
s = original
s['123']='TEST'
print(s,"\n")
s = original
s.sub!('123','TEST')
print(s,"\n")

will output

stringtest.rb:4:in `[]=': can't modify frozen string (TypeError)
        from stringtest.rb:4

That is just plain wonderful. We are still on the same place: nowhere. What would be the solution? Nothing sane is available. You have to use s = String.new(original) instead of simple assignment. This is a terrible looking pain in the ass solution.

Who the hell knows where was my string declared at the first time? Who knows what will be broken if I change a string I got from somewhere? Who will find the real problem for an error message like File not found: 'TEST'?

Unexpected behavior: pointer to constant

Preface: some words about correct 'const' syntax

The general rule is that the const keyword affects its immediate left neighbor. Sic! So the correct syntax for defining a pointer to a constant integer is int const * pInteger. The history proved that the traditional style is not sufficient, but is still maintained: If the const keyword is the leftmost in a type specification then it affects its immediate right neighbor.

Constants are to be disposed too

#include <iostream>
class A {
public:
        A(){ std::cout << "Risen #" << (idx=++counter) << std::endl; }
        ~A(){ std::cout << "Fallen #" << idx << std::endl; }
private:
        int idx;
        static int counter;
};
int A::counter = 0;

int main(){
        A const first;
        return 0;
}

will output (as expected)

Risen #1
Fallen #1

As we can observe, the destructor of the const-qualified first variable was called. That extrapolates that the const qualifier does not protect from calling the destructor on a pointer which is a weird looking thing for the first time.

The unexpected behavior

#include <iostream>
class A { /* same as the above */ };
int A::counter = 0;
void f(A const * pTest){ delete pTest; }

int main(){
        A *pFirst = new A, second;
        f(pFirst);
        A const third;
        return 0;
}

will compile flawlessly and will produce

Risen #1
Risen #2
Fallen #1
Risen #3
Fallen #3
Fallen #2

The bad idea

Let's make it impossible to call a delete on pointers to constants! Bad idea. The following example must be possible.

Vector2D const * pVector = new Vector2D(3,2);
// ...
delete pVector; // <--- This is it.

And the deletion of a pointed value must be delegable to functions. That's why the f() was able to delete its parameter.

One may feel unsafe at this moment, but it is not really a problem in the industry: almost nobody has the clue that it is even possible, and nobody wants to do that anyways, except when it is the main goal. But then it's not a trap.