Iterating a list of objects with foreach

Question

I came across this statement:

"When using foreach on a list of objects, the iterated object instance is not editable, but the object properties are editable"

Could someone demonstrate the above with a simple example, please?

Let me re-phrase (as I found the statement in two versions), maybe this statement is more clear:

"When using foreach on a list of elements, the iteration variable that provides the element is readonly, but the element properties are editable"

Sabin

It means the list itself cannot be modified (you cannot remove or add items while you are in the loop), but the properties of the items in the list can be modified. Also read #4005255 – Withdrawn

where did you find that quote? – Myopic

I found that in a course about C# generic types in PS (PS is the abbreviation of a well known online courses provider) – Sabin

Answer 1

foreach(var foo in foos)
{
  foo = null; // WRONG, foo is not editable
  foo.name = "John";  // RIGHT, foo properties are editable
}

Immolate

Doesnt foo.name = "John" modify the object instance?? (so the instance IS editable) – Sabin

@cnom, it looks like you simply don't understand what is instance. – Extraterritoriality

"...object instance is not editable, but the object properties are editable..." = "...foo is not editable, but foo.name are editable..." – Immolate

Sorry for the question, but some comments in other answers mixed things up... Is foo, or foos the iterated object? – Sabin

foos is a collection of foo – Immolate

You cannot either modify the collection foos without throwing an InvalidOperationException – Ilianailine

@Stanley , my question is "What is the iterated object", not what is foos – Sabin

@Sabin foos is the iterated object. More specifically, the iterated collection – Ilianailine

Example: foo[] foos = new foo[] {foo1, foo2, foo3, ...}; – Immolate

@Stanley, so that example, does not demonstrate what I asked for. It is modifying foo, not the iterated object, in this case Lee's example demonstrates it more clearly! – Sabin

@Sabin - It's difficult to answer this question without a concrete example, but it is possible that the terminology in the original statement is wrong. This answer demonstrates that the iteration variable cannot be modified, but the object instance it currently refers to can be mutated through it. – Pullover

Answer 2

What is means is that the items in the list can't change whilst iterating, but the contents of the items may.

this will alter the collection and prevent the foreach completing:

foreach(var item in collection)
{
   collection.Remove(item);
}

This will change an item in the list and not prevent the foreach completing:

foreach(var item in collection)
{
    item.name = "Neil";
}

Konrad

this second snippet refers to the list, not the iterated object! – Sabin

@Sabin the second snippet refers to the object, not the list ! – Konrad

Sorry i meant the opposite, the first snippet refers to the list... :) – Sabin

Answer 3

Yes

Foreach (n in list) if (n.something==true) list.Remove(n);

this will fail

you cannot remove an item in list, unlike say a for loop

Frontward

Answer 4

foreach var car in cars 
{
    //you can edit car.color here
    //you cannot edit car
}

Candelaria

Answer 5

Not sure you need an example for this. You will step over each object in the collection, and you can do what you like to each of those objects, but you can't make changes to the collection itself, e.g. Insert, Remove, Clear, etc. Attempting such will throw an exception.

Husbandry