CODEWITHSUNDEEP
.net
k3b
k3b

Reputation: 14755

.net Naming convention: Is there a semantic difference between Length and Count?

In order to to get the number of subitems in dotnet sometimes i have to ask a property Lenght sometimes i have to ask a property Count.

Is there any reason for the distinction?

example:

   int[] a; if (a.Length == 0) ....
   IList<int> b; if (b.Count == 0) ....

Note Difference between IEnumerable Count() and Length sounds similar but does not answer the semantic between Length and Count

Upvotes: 3

Views: 222

Answers (5)

Hans Kesting
Hans Kesting

Reputation: 39284

I can't quote a source, but I think that a .Length is a fixed value and a .Count can change.

You can't change the number of items in an array once it is created, so that has a .Length.

You can add to (or remove from) a List, so that has a .Count.

EDIT
So a .Length:

  • Will not change for this object
  • Should involve just a quick lookup of an internal value

While a .Count or .Count():

  • Might change for this object
  • Might involve an iteration over the internal items (depending on the implementation)

Upvotes: 5

Steven
Steven

Reputation: 172676

I can remember the Framework Design Guidelines contains an annotation about this difference (I will at a qoute of it tomorrow). What I recall is that the designers think this is a quirk in the design, because it doesn't make sense for a lot of developers. Remember that in the beginning there were no design guidelines for .NET and much of the .NET API was copied from Java, including the quirks.

Upvotes: 1

Andrei Pana
Andrei Pana

Reputation: 4502

Semantically, an array has a constant number of elements, it has a length, therefore the property is called Length. A list has variable number of elements, and if you want to know how many elements are there, you need to count them, therefore the Count name.

Upvotes: 3

Oded
Oded

Reputation: 499072

Length is an array property, Count an ICollection one and Count() a method on IEnumerable, but aside from that, they mean the same.

That is, they hold that number of items in the collection.

Note: in the case of IEnumerable, the Count() method can (and normally will) iterate over all items in the collection in order to obtain a count. The properties will simply return a value.

Upvotes: 2

Darin Dimitrov
Darin Dimitrov

Reputation: 1038930

There's no semantic difference. It just a framework design detail that we should deal with.

Upvotes: 2

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