IEnumerable vs. List in C#: When Should You Choose Which?

The differences and performance effects of IenuMerable and List in the c#

When treating the collection in C#, the difference between

and

is very important. IEnumerable Represents a enumerator, which provides a method of traversing the collection; List is the specific implementation of the IEnumerable interface. List IEnumerable Consider the following two Linq query:

The working principle of the enumerator

<code class="language-csharp">List<animal> sel1 = (from animal in Animals 
                    join race in Species
                    on animal.SpeciesKey equals race.SpeciesKey
                    select animal).Distinct().ToList();

IEnumerable<animal> sel2 = (from animal in Animals 
                           join race in Species
                           on animal.SpeciesKey equals race.SpeciesKey
                           select animal).Distinct();</code>

When using , debugging will show members such as "Inner" and "OUTER", which may be confusing. "Inner" members include objects from the connection set (Species), and "OUTER" members include objects from the initial set (Animal). Query using these members to perform the connection operation.

Performance considerations

IEnumerable

In terms of performance,

is usually more favored because it is delayed until the enumeration query. Using will be forced to calculate and specific results immediately, which may limit optimization opportunities. But if you need to perform a query multiple times, it will be converted to

more efficient, because it can prevent calculating query each time.

IEnumerable Use scene ToList()

Applicable to the following situation: List

Want to delay the execution until later. Want to optimize query performance.

Multiple iterations may be required. IEnumerable

Applicable to the following situation:
• You need to prevent queries from being executed many times.
• Want to use specific collection objects.

Need to access unavailable members.

List

Conclusion

The selection between and
• depends on the specific requirements of the application. For delayed execution and performance optimization, please use
; and when you need to calculate or specific collection function immediately, use
• . IEnumerable

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