SortedList sl = new SortedList();
sl.Add(2, 5);
sl[2] = (int)sl[2]+ 1;
Console.WriteLine(sl[2]);
[.net] boxing!?
Author
I don't understand why this outputs "6":
I thought sl[2] would return a boxed copy of the number there, but itappears that it returns an actual reference. What is happenning?
Well, sl[2] is initially 5 because of your Add() call, so sl[2]+1 is 6, and you store that back in sl[2] and print it out.
Author
Yes, but I thought that when you box and unbox you are only making copies.
Maybe this is what is happening?:
When 5 is Added to the list, it is added onto the heap "in a box". The indexer returns a reference to that box, which is then changed.
Is that right?
Maybe this is what is happening?:
When 5 is Added to the list, it is added onto the heap "in a box". The indexer returns a reference to that box, which is then changed.
Is that right?
You're overwriting 5 with 6. The fact that the value 6 is wrapped in an object before it's put in the SortedList shouldn't be a source of confusion for you - what are you expecting the value to be and why?
Author
I thought it should be 5:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/csref/html/vclrfboxingconversionpg.asp
Edit: I don't know how to link. :(
That article shows the boxed value being seperate from the unboxed value.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/csref/html/vclrfboxingconversionpg.asp
Edit: I don't know how to link. :(
That article shows the boxed value being seperate from the unboxed value.
For links, use the same code as plain HTML:
{a href="url..."}text for the link{/a}
(replace { with <).
For your question, I think that you don't realize that the assignment operator overwrites what's in sl[2]. Here's the details:
1. sl.Add(2, 5) adds a boxed 5 in s1;
2. sl[2] returns the boxed 5;
3. (int) unbox the 5;
4. + 1 returns the value 6;
5. the = assignment boxes the 6, and stores the boxed 6 in sl[2];
6. sl[2] returns the boxed 6;
7. WriteLine prints it on the console.
I hope things are more clear now.
Best,
jods
{a href="url..."}text for the link{/a}
(replace { with <).
For your question, I think that you don't realize that the assignment operator overwrites what's in sl[2]. Here's the details:
1. sl.Add(2, 5) adds a boxed 5 in s1;
2. sl[2] returns the boxed 5;
3. (int) unbox the 5;
4. + 1 returns the value 6;
5. the = assignment boxes the 6, and stores the boxed 6 in sl[2];
6. sl[2] returns the boxed 6;
7. WriteLine prints it on the console.
I hope things are more clear now.
Best,
jods
Author
Yep, sl[2] returns the boxed value which is already being stored, which is why the changes stay. Thanks for clarifying. [grin]
This topic is closed to new replies.
Advertisement
Popular Topics
Advertisement
