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IList<T> is not necessarily representative of the general case; it's an interface that is (A) widely implemented by a variety of classes from a variety of sources, which themselves (B) tend t...
Answer
#2: Post edited
by
r~~
·
2023-01-09T16:37:35Z (almost 2 years ago)
`IList<T>` is not necessarily representative of the general case; it's an interface that is (A) widely implemented by a variety of classes from a variety of sources, which themselves (B) tend to add additional functionality or constraints not captured by the signature of `IList<T>`. There is, in my opinion, very little if any reason to ever return a `List<T>` instead of an `IList<T>`, but you could very well want to return a `SortedSet<T>` in order to get at its `Min` and `Max` properties.- Ideally, for that example, there'd be some sort of `ISortedSet<T>` interface that would abstract over those properties. But there isn't, as of .NET 7.0, which historically is representative of the story with these abstract collection interfaces. Good ideas, 80% execution. So in practice, sometimes you want to type things concretely.
- For interfaces that don't get around as much, like ye olde `IMyInternalApplicationService`, you won't go wrong always favoring those over their concrete implementations everywhere in your code except the place where you tie off your dependency injection knots.
- `IList<T>` is not necessarily representative of the general case; it's an interface that is (A) widely implemented by a variety of classes from a variety of sources, which themselves (B) tend to add additional functionality or constraints not captured by the signature of `IList<T>`. There is, in my opinion, very little <s>if any</s> [see below for one] reason to ever return a `List<T>` instead of an `IList<T>`, but you could very well want to return a `SortedSet<T>` in order to get at its `Min` and `Max` properties.
- Ideally, for that example, there'd be some sort of `ISortedSet<T>` interface that would abstract over those properties. But there isn't, as of .NET 7.0, which historically is representative of the story with these abstract collection interfaces. Good ideas, 80% execution. So in practice, sometimes you want to type things concretely.
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- Peter Taylor adds: ‘Another issue specific to `IList<T>` is that for legacy reasons it doesn't inherit from `IReadOnlyList<T>`. Returning `List<T>` allows callers to assign to `IReadOnlyList<T>`, which can make it easier to reason about the calling code.’
- ---
- For interfaces that don't get around as much, like ye olde `IMyInternalApplicationService`, you won't go wrong always favoring those over their concrete implementations everywhere in your code except the place where you tie off your dependency injection knots.
#1: Initial revision
by
r~~
·
2022-12-22T00:09:38Z (almost 2 years ago)
`IList<T>` is not necessarily representative of the general case; it's an interface that is (A) widely implemented by a variety of classes from a variety of sources, which themselves (B) tend to add additional functionality or constraints not captured by the signature of `IList<T>`. There is, in my opinion, very little if any reason to ever return a `List<T>` instead of an `IList<T>`, but you could very well want to return a `SortedSet<T>` in order to get at its `Min` and `Max` properties. Ideally, for that example, there'd be some sort of `ISortedSet<T>` interface that would abstract over those properties. But there isn't, as of .NET 7.0, which historically is representative of the story with these abstract collection interfaces. Good ideas, 80% execution. So in practice, sometimes you want to type things concretely. For interfaces that don't get around as much, like ye olde `IMyInternalApplicationService`, you won't go wrong always favoring those over their concrete implementations everywhere in your code except the place where you tie off your dependency injection knots.