I am using an ArrayList named "nodeRanks" of the following structs:

private struct NodeRank
{
public TreeNode Node;
public Int32 Rank;
}

I sort the nodeRanks ArrayList based upon the rank values, and then I would
like to replace the rank values with the ArrayList index values. However,
when I try the following approach, I get a runtime error:

for(int i=0;i<=nodeRank.Count-1;i++)
{
((NodeRank)nodeRanks[i]).rank = i;
}

The error that I get is: (3696): The left-hand side of an assignment must
be a variable, property or indexer

I am not sure why I am getting this error because the left side of my
assignment is a public field (variable) of the struct. If I re-write the
code as follows, it works. But I would still like to know why the more
consise syntax fails.

NodeRank tempNodeRank;
for(int i=0;i<=nodeRank.Count-1;i++)
{
tempNodeRank = (NodeRank)nodeRanks[i];
tempNodeRank.rank = i;
nodeRanks[i] = tempNodeRank;
}

Thanks!!

craig wrote:
> I am using an ArrayList named "nodeRanks" of the following structs:
>
> private struct NodeRank
> {
> public TreeNode Node;
> public Int32 Rank;
> }
>
> I sort the nodeRanks ArrayList based upon the rank values, and then I
> would like to replace the rank values with the ArrayList index
> values. However, when I try the following approach, I get a runtime
> error:
> for(int i=0;i<=nodeRank.Count-1;i++)
> {
> ((NodeRank)nodeRanks[i]).rank = i;
> }
>
> The error that I get is: (3696): The left-hand side of an assignment
> must be a variable, property or indexer
>
> I am not sure why I am getting this error because the left side of my
> assignment is a public field (variable) of the struct. If I re-write
> the code as follows, it works. But I would still like to know why
> the more consise syntax fails.
>
> NodeRank tempNodeRank;
> for(int i=0;i<=nodeRank.Count-1;i++)
> {
> tempNodeRank = (NodeRank)nodeRanks[i];
> tempNodeRank.rank = i;
> nodeRanks[i] = tempNodeRank;
> }
>
> Thanks!!

I think it works when you change NodeRank to a "class".
ArrayList stores *objects*, which means that structs (as value-types)
are boxed. This is a copy(-like) operation, as there are no references
to value-types. So you original code would update a copy of the
"real" value, and then discard that copy. The version in the ArrayList
is not updated.

Hans Kesting

NodeRank is a struct, so it's a value type.
ArrayList holds objects, which are reference types.

To store a value type in a object, it must be boxed.

Writing "tempNodeRank = (NodeRank)nodeRanks[i];" unboxes the struct.
"((NodeRank)nodeRanks[i]).rank" is attempting to refernce the still
boxed object.

Change NodeRank to a class, and that line will work.

--
Truth,
James Curran
[erstwhile VC++ MVP]
Home: www.noveltheory.com Work: www.njtheater.com
Blog: www.honestillusion.com Day Job: www.partsearch.com


"craig" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I am using an ArrayList named "nodeRanks" of the following structs:
>
> private struct NodeRank
> {
> public TreeNode Node;
> public Int32 Rank;
> }
>
> I sort the nodeRanks ArrayList based upon the rank values, and then I
would
> like to replace the rank values with the ArrayList index values. However,
> when I try the following approach, I get a runtime error:
>
> for(int i=0;i<=nodeRank.Count-1;i++)
> {
> ((NodeRank)nodeRanks[i]).rank = i;
> }
>
> The error that I get is: (3696): The left-hand side of an assignment must
> be a variable, property or indexer
>
> I am not sure why I am getting this error because the left side of my
> assignment is a public field (variable) of the struct. If I re-write the
> code as follows, it works. But I would still like to know why the more
> consise syntax fails.
>
> NodeRank tempNodeRank;
> for(int i=0;i<=nodeRank.Count-1;i++)
> {
> tempNodeRank = (NodeRank)nodeRanks[i];
> tempNodeRank.rank = i;
> nodeRanks[i] = tempNodeRank;
> }
>
> Thanks!!
>
>
>
>
>

Thanks! I forgot about boxing.

"James Curran" <(E-Mail Removed)> wrote in message
news:%23XrQe$(E-Mail Removed)...
> NodeRank is a struct, so it's a value type.
> ArrayList holds objects, which are reference types.
>
> To store a value type in a object, it must be boxed.
>
> Writing "tempNodeRank = (NodeRank)nodeRanks[i];" unboxes the struct.
> "((NodeRank)nodeRanks[i]).rank" is attempting to refernce the still
> boxed object.
>
> Change NodeRank to a class, and that line will work.
>
> --
> Truth,
> James Curran
> [erstwhile VC++ MVP]
> Home: www.noveltheory.com Work: www.njtheater.com
> Blog: www.honestillusion.com Day Job: www.partsearch.com
>
>
> "craig" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
>> I am using an ArrayList named "nodeRanks" of the following structs:
>>
>> private struct NodeRank
>> {
>> public TreeNode Node;
>> public Int32 Rank;
>> }
>>
>> I sort the nodeRanks ArrayList based upon the rank values, and then I
> would
>> like to replace the rank values with the ArrayList index values.
>> However,
>> when I try the following approach, I get a runtime error:
>>
>> for(int i=0;i<=nodeRank.Count-1;i++)
>> {
>> ((NodeRank)nodeRanks[i]).rank = i;
>> }
>>
>> The error that I get is: (3696): The left-hand side of an assignment
>> must
>> be a variable, property or indexer
>>
>> I am not sure why I am getting this error because the left side of my
>> assignment is a public field (variable) of the struct. If I re-write the
>> code as follows, it works. But I would still like to know why the more
>> consise syntax fails.
>>
>> NodeRank tempNodeRank;
>> for(int i=0;i<=nodeRank.Count-1;i++)
>> {
>> tempNodeRank = (NodeRank)nodeRanks[i];
>> tempNodeRank.rank = i;
>> nodeRanks[i] = tempNodeRank;
>> }
>>
>> Thanks!!
>>
>>
>>
>>
>>
>
>