Re: Switch and case syntax restriction

From: ("Nevin :-] Liber")
Sat, 20 Oct 2007 17:31:34 GMT
In article <4t7Si.11734$>, (Henrik Andersson) wrote:

Nevin :-] Liber wrote:

struct MyInt
   operator int() const { return i + 1; }

   bool operator==(int j) const { return i == j; }

   int i;


MyInt mi;
switch (mi)
case 1:
case 2:

Same as:
if(mi==1) {
} else if(mi==2) {

The operator(int) is not invoked, since the operator== got a specific
prototype for this case. This is different from how it currently would work!

And you still believe there would be any chance of getting this into the
standard? Breaking backwards compatibility (and silently at that) is
not something the committee ever takes lightly.

It's even worse. Many times switch is implemented as O(1) or O(log n),
depending on the density of the labels. Your pessimization is O(n),
unless you have inlining and aggressive optimization.

I think that it would be a rather bad design if this semantic change
would effect any program.

That is irrelevant. Your change silently breaks existing, working
programs. Even if it doesn't break them, it slows them down.

I must admit that I did not know of the conversation operators, but you
never stop learning.

If you wish to propose language changes, you really need to learn the
language in depth.

Worse, it make all switch statements harder to read, as
one now has to understand the type of every label and variable being
switched upon before I know its semantics.

If people stopped doing crazy operator overloadings, the problem would
be void.

There are lots of reasons people overload operators, which have nothing
to do with being crazy. For instance, people will add an operator< to
their class so that they can be easily stored in a set or as a key in a
map, even though an ordering makes no other sense for the class.

 Nevin ":-)" Liber <> 773 961-1620

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