Re: [Boost-users] [multiindex] hashed index, modify() and traversal

From: Francesco Biscani (bluescarni_at_[hidden])
Date: 2006-10-27 09:26:04

Hi Joaquín,

first of all thanks for your answers. I find your replies always very 
helpful :)

I think I've understood what you mean. Just let me recap to see if I got it 
right.

1. There are two ways to make sure a modification with traversal is 
successful:

2. I can traverse an index (hashed or ordered, it does not matter) to modify() 
all the elements of the container if I am sure that the modification does not 
change the representation of the elements with respect to the index I'm 
traversing on.
2a. For example, I can use the hashed index for traversing whenever I'm sure 
that the modifications won't change the hash value of the elements.
2b. Or I can use an ordered index whenever I'm sure that the modification does 
not change the position of the element in the binary search tree.

3. I can also traverse and modify an ordered index from top to bottom if I'm 
consistently modifying each element to place itself _higher_ in the tree than 
it was before. In the opposite way I can traverse bottom to top if I'm 
consistently modifying the element to be _lower_ in the tree.

So, in my case I was using an hashed index traversal while I was changing the 
hash values. It's a no-go. However I also have an ordered index already 
defined, and the modification I want to do does not change the ordering of 
elements. Hence the use of a sorted index for this purpose is safe.

Does this make sense? :)

Thanks again,

  Francesco