Hooked on LINQ

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Namespace:System.Linq
Assembly:System.Core.dll
Extends:IEnumerable<T>

Back to Standard Query Operator Index


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Introduction

The Last operator returns the last element of a sequence.

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Method Signatures

// 1 - Return the last element in a sequence.
public static TSource Last<TSource>(
    this IEnumerable<TSource> source)
 
// 2 - Return the last element in a sequence that matches this predicate.
public static TSource Last<TSource>(
    this IEnumerable<TSource> source, 
    Func<TSource, bool> predicate)



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Exceptions

Throws an ArgumentNullException if source or predicate is null.
Throws an InvalidOperationException if source is empty, or there is no matching element found for the predicate.


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Pseudo-code

Overload 1
If source is null, throw an ArgumentNullException.
If the source sequence implements IList<T>, then
If the source sequence is empty throw InvalidOperationException.
Return source[count - 1]. (performance optomization)
Else Iterate the source sequence.
If there is no elements at all, throw InvalidOperationException.
If this is the last element, return it as the result.

Overload 2
If source is null, throw an ArgumentNullException.
If predicate is null, throw an ArgumentNullException.
Iterate the source sequence.
If predicate(current element) returns true, remember current element.
If no matching element was found.
Throw an InvalidOperationException.
Else
Return the last element that passed the predicate function.

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Loop Count

Overload 1
< 1 If the collection is of type IList, then the first element is accessed by index position which is different depending on the collection implementation; Otherwise, Loop count = 1 as the entire sequence is iterated to find the last element.


Overload 2
1. The entire source sequence is iterated, and the last matching element is returned.


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Code Samples

TODO: Needs code sample.

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