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From: Bob Altman on 1 Jul 2008 16:11
Hi all,

I'm trying to do something that should be really easy, but I can't think of an
obvious way to do it. I have a dictionary whose value is a "value type" (as
opposed to a reference type -- in this case, a Boolean):

Dim dic As New Dictionary(Of Int32, Boolean)
dic(123) = True

I want to set all of the existing entries in the dictionary to False. The
obvious solution:

For Each value As Boolean In dic.Values
value = False
Next

does not set the dictionary values to False as one would expect. Rather, this
code gets a temp variable named value and sets that temp variable to false,
leaving the dictionary value unchanged.

Ok, so I try this code:

For Each key As Int32 In dic.Keys
dic(key) = False
Next

That gets me the dreaded "Collection was modified; enumeration operation may not
execute."

So, how can I set all of the Boolean values in this dictionary to False?

TIA - Bob


From: Family Tree Mike on 1 Jul 2008 17:06
It seems to me that you should just check if the dictionary does not contain
the key, assume false. You should not need to fill the dictionary with
every possibility.

dict.ContainsKey(123), for example.


"Bob Altman" <rda(a)nospam.nospam> wrote in message
news:ernaia72IHA.2424(a)TK2MSFTNGP04.phx.gbl...
> Hi all,
>
> I'm trying to do something that should be really easy, but I can't think
> of an obvious way to do it. I have a dictionary whose value is a "value
> type" (as opposed to a reference type -- in this case, a Boolean):
>
> Dim dic As New Dictionary(Of Int32, Boolean)
> dic(123) = True
>
> I want to set all of the existing entries in the dictionary to False. The
> obvious solution:
>
> For Each value As Boolean In dic.Values
> value = False
> Next
>
> does not set the dictionary values to False as one would expect. Rather,
> this code gets a temp variable named value and sets that temp variable to
> false, leaving the dictionary value unchanged.
>
> Ok, so I try this code:
>
> For Each key As Int32 In dic.Keys
> dic(key) = False
> Next
>
> That gets me the dreaded "Collection was modified; enumeration operation
> may not execute."
>
> So, how can I set all of the Boolean values in this dictionary to False?
>
> TIA - Bob
>

From: Kerry Moorman on 1 Jul 2008 17:08
Bob,

While we're wating for the elegant solution, here's abrute force solution:

Dim myKeysArray(dic.Keys.Count - 1) As Integer
dic.Keys.CopyTo(myKeysArray, 0)

For Each key As Integer In myKeysArray
dic(key) = False
Next

Kerry Moorman


"Bob Altman" wrote:

> Hi all,
>
> I'm trying to do something that should be really easy, but I can't think of an
> obvious way to do it. I have a dictionary whose value is a "value type" (as
> opposed to a reference type -- in this case, a Boolean):
>
> Dim dic As New Dictionary(Of Int32, Boolean)
> dic(123) = True
>
> I want to set all of the existing entries in the dictionary to False. The
> obvious solution:
>
> For Each value As Boolean In dic.Values
> value = False
> Next
>
> does not set the dictionary values to False as one would expect. Rather, this
> code gets a temp variable named value and sets that temp variable to false,
> leaving the dictionary value unchanged.
>
> Ok, so I try this code:
>
> For Each key As Int32 In dic.Keys
> dic(key) = False
> Next
>
> That gets me the dreaded "Collection was modified; enumeration operation may not
> execute."
>
> So, how can I set all of the Boolean values in this dictionary to False?
>
> TIA - Bob
>
>
>
From: Armin Zingler on 1 Jul 2008 16:28
"Bob Altman" <rda(a)nospam.nospam> schrieb
> So, how can I set all of the Boolean values in this dictionary to
> False?

For Each key In dic.Keys.ToArray
dic(key) = False
Next



Armin
From: Tom Shelton on 1 Jul 2008 18:10
On 2008-07-01, Bob Altman <rda(a)nospam.nospam> wrote:
> Hi all,
>
> I'm trying to do something that should be really easy, but I can't think of an
> obvious way to do it. I have a dictionary whose value is a "value type" (as
> opposed to a reference type -- in this case, a Boolean):
>
> Dim dic As New Dictionary(Of Int32, Boolean)
> dic(123) = True
>
> I want to set all of the existing entries in the dictionary to False. The
> obvious solution:
>
> For Each value As Boolean In dic.Values
> value = False
> Next
>
> does not set the dictionary values to False as one would expect.

Just a small comment, since you have received a solution - but, the observed
behavior is EXACTLY what is to be expected... Booleans are value types - and
so on any assignment, a copy is made. It's basically the same as:

Dim b1 As Boolean = True
Dim b2 As Boolean = b1

Console.WriteLine ("b1 = {0}, b2={1}", b1, b2)
b1 = False
Console.WriteLine ("b1 = {0}, b2={1}", b1, b2)

--
Tom Shelton
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