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Remove ICollection<T> as an allowed interface from AV1130 #216

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Merged
dennisdoomen merged 1 commit into from
Aug 17, 2020
Merged

Remove ICollection<T> as an allowed interface from AV1130 #216

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6 changes: 2 additions & 4 deletions _rules/1130.md
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Original file line number Diff line number Diff line change
@@ -1,11 +1,9 @@
---
rule_id: 1130
rule_category: member-design
title: Return an `IEnumerable<T>` or `ICollection<T>` instead of a concrete collection class
title: Return interfaces to unchangeable collections
severity: 2
---
You generally don't want callers to be able to change an internal collection, so don't return arrays, lists or other collection classes directly. Instead, return an `IEnumerable<T>`, or, if the caller must be able to determine the count, an `ICollection<T>`.

**Note:** If you're using .NET 4.5 or higher, you can also use `IReadOnlyCollection<T>`, `IReadOnlyList<T>` or `IReadOnlyDictionary<TKey, TValue>`.
You generally don't want callers to be able to change an internal collection, so don't return arrays, lists or other collection classes directly. Instead, return an `IEnumerable<T>`, `IReadOnlyCollection<T>`, `IReadOnlyList<T>` or `IReadOnlyDictionary<TKey, TValue>`.

**Exception:** Immutable collections such as `ImmutableArray<T>`, `ImmutableList<T>` and `ImmutableDictionary<TKey, TValue>` prevent modifications from the outside and are thus allowed.