JuniorTheoryCommon

What does the program print?

List<int> nums = [1, 2, 3];
var big = nums.Where(n => n > 1);
List<int> copy = big.ToList();
nums.Add(4);
Console.WriteLine($"{big.Count()} {copy.Count}");

3 2

Expecting 2 2: Where does not filter on its own line; the query runs when Count() enumerates it, after 4 was added.
Expecting ToList() to stay linked to the list: it runs the query at once and stores a separate list that later changes do not reach.

What does the program print if nums.Clear(); replaces nums.Add(4);?
Why does changing nums inside a foreach over big throw an exception?

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JuniorTheoryCommon

What does the program print?

List<int> nums = [1, 2, 3];
var big = nums.Where(n => n > 1);
List<int> copy = big.ToList();
nums.Add(4);
Console.WriteLine($"{big.Count()} {copy.Count}");

3 2

Expecting 2 2: Where does not filter on its own line; the query runs when Count() enumerates it, after 4 was added.
Expecting ToList() to stay linked to the list: it runs the query at once and stores a separate list that later changes do not reach.

What does the program print if nums.Clear(); replaces nums.Add(4);?
Why does changing nums inside a foreach over big throw an exception?

Back to questions Open topic in roadmap →Answer it yourself — Quiz