why foreach does always have to declare a new variable

  • Thread starter Thread starter cody
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cody

why foreach does always have to declare a new variable?
I have to write

foreach (int n in array){}

but Iam not allowed to write:

int n=0;
foreach (n in array){}

what is the reasoning behind that?
 
cody said:
why foreach does always have to declare a new variable?
I have to write

foreach (int n in array){}

but Iam not allowed to write:

int n=0;
foreach (n in array){}

what is the reasoning behind that?
Click to expand...

I don't have a definitive answer, but I can give some fairly good answers.

One thing is that it helps avoids silly mistakes like
string item;
.... //code that uses item
foreach(item in Items)
{
}

Also, since the variable is always assigned to, there is no value in
allowing pre-existing assignment.
int n = 0;
foreach (n in array)

will *never* use n as it is, instead assinging from the array, thus there is
no real reason to allow it.

And, finally, since foreach *does* result in a cast, defining the type
directly within the foreach statement makes code much clearer.
 
why foreach does always have to declare a new variable?
I don't have a definitive answer, but I can give some fairly good answers.

One thing is that it helps avoids silly mistakes like
string item;
... //code that uses item
foreach(item in Items)
{
}

Also, since the variable is always assigned to, there is no value in
allowing pre-existing assignment.
int n = 0;
foreach (n in array)
Click to expand...

That is right but the code was meant that the variable n could be used by
other code either before or after the loop in which case it would have to be
explicitly assigned to.
And, finally, since foreach *does* result in a cast, defining the type
directly within the foreach statement makes code much clearer.
Click to expand...

Thinking about it this sounds very very reasonable :)

I've never liked the implicit cast in foreach loops because it is very
dangerous and once we have generics it will be very superflous too.

My proposal is that in csc 2.0 there should be an option that if foreach
loop variable would require an implicit cast, a warning is outputted.
Additionally, when using a generic IEnumerator in the foreach loop, the
warning is *always* outputted, no matter what the compiler settings are.
e.g

IList list = new ArrayList();
foreach (string s in list) // warning is outputted only if compilersetting
is set

IList<object> list = new ArrayList<object>();
foreach (string s in list) // a warning is always issued
 
Also, since the variable is always assigned to, there is no value in
That is right but the code was meant that the variable n could be used by
other code either before or after the loop in which case it would have to
be
explicitly assigned to.
Click to expand...

Yes, but its a waste, IMHO. It makes code more confusing, I would probably
consider any code using that pattern as fragile at best, badly written more
likely.
Thinking about it this sounds very very reasonable :)

I've never liked the implicit cast in foreach loops because it is very
dangerous and once we have generics it will be very superflous too.

My proposal is that in csc 2.0 there should be an option that if foreach
loop variable would require an implicit cast, a warning is outputted.
Additionally, when using a generic IEnumerator in the foreach loop, the
warning is *always* outputted, no matter what the compiler settings are.
Click to expand...

Yes, I know. And as I said the last time you suggested this, I think its
unimportant, especially since you're the first person I've seen complain
about it.

I really don't agree that the implicit cast is dangerous by any degree, its
only implicit if you a) don't know what you are doing, or b) allow code like
you recommend without the type specifier. The behaviour is sane and pretty
clear, IMHO.
 
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