C# Func vs Expression>

Question

In C#, given that:

IEnumerable<T> declares Where(Func<T, bool>)
IQueryable<T> extends IEnumerable<T>
IQueryable<T> declares Where(Expression<Func<T, bool>>))

When using this:

var list = new List<int>();
var positives = list.AsQueryable().Where(x => x > 0);

How does the C# compiler distinguish between both methods?

["Closer is better"](https://ericlippert.com/2013/12/23/closer-is-better/). — 15ee8f99-57ff-4f92-890c-b56153, Sep 19 '19 at 14:45
The standard rules of method resolution apply. `list.AsQueryable()` has type `IQueryable`, so `IQueryable.Where` is used. If you tried the same thing with both methods declared on the same type, the call would be ambiguous. — Jeroen Mostert, Sep 19 '19 at 14:47
@EdPlunkett Yes I agree, but why is `x => x > 0` closer to `Expression>` than `Func` ? — Spiff, Sep 20 '19 at 00:49
@Spiff It isn’t. If both methods were defined in the same class, the overload couldn’t be resolved (try it). You’re asking the wrong question. Read the article. Or mm8’s answer. — 15ee8f99-57ff-4f92-890c-b56153, Sep 20 '19 at 00:50

score 1 · Accepted Answer · answered Sep 19 '19 at 14:47

1

The overload of Where that accepts an Expression<Func<T, bool>> is an extension method of IQueryable<T> and since IQueryable<T> extends IEnumerable<T>, it will be chosen first due to the overload resolution mechanism in C#.

Please refer to @Jon Skeet's article on the subject for more information:

If there are two methods at different levels of the hierarchy, the "deeper" one will be chosen first ...

answered Sep 19 '19 at 14:47

mm8

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Why the downvotes? This is correct, isn't it? – FreezyLemon Sep 19 '19 at 14:51

C# Func vs Expression>

1 Answers1