Deconstruct for interface

[WeihanLi]

Is it possible to use deconstruct for an interface?

For example, we could use deconstruct for Dictionary, is it possible to use deconstruct for IDictionary?

var dic = new Dictionary<string, string>();
foreach (var (key, value) in dic)

[HaloFour]

The short answer is yes, any type can support custom deconstruction via extension methods.

However, if you're referring to the non-generic System.Collections.IDictionary this is complicated by the fact that it implements System.Collections.IEnumerable which effectively enumerates all values as System.Object. An extension method to deconstruct System.Object is possible but wouldn't apply in most situations, so what I might suggest is an extension method on IDictionary that returns IEnumerable<DictionaryEntry> which would be safe to deconstruct:

public static class IDictionaryExtensions {
    // returns a type-safe enumerable of each entry
    public static IEnumerable<DictionaryEntry> Entries(this IDictionary dictionary) {
        foreach (DictionaryEntry entry in dictionary) {
            yield return entry;
        }
    }
    
    // deconstruct each entry
    public static void Deconstruct(this DictionaryEntry entry, out object key, out object value) {
        key = entry.Key;
        value = entry.Value;
    }
}

Then you can use it like this:

IDictionary dictionary = ...;

foreach (var (key, value) in dictionary) {
    // ...
}

However, the key and value will both be of type System.Object.