Helper to enumerate IConfiguration?

[davidfowl]

I was trying to copy an IConfiguration into a flat dicitonary and came up with this (completely untested) method:

var stack = new Stack<IConfiguration>();
stack.Push(configuration);

while (stack.Count > 0)
{
    var config = stack.Pop();
    var section = config as IConfigurationSection;

    if (section != null)
    {
        yield return new KeyValuePair<string, string>(section.Path, section.Value);
    }

    foreach (var child in config.GetChildren())
    {
        stack.Push(child);
    }
}

It would be useful to have something that expanded all of the kvps without doing manual recursion.

/cc @divega @HaoK

[divega]

Looks good!

I was trying to copy an IConfiguration into a flat dicitonary

Curious, do you see this as something many customers will need to do or as a rather advanced scenario?

FWIW, we could have had IConfiguration: IEnumerable<KeyValuePair<string, string>> directly but decided against it to avoid some unwanted side effects (like having the full set of LINQ operators show up in Intellisense). We could have an extension method for this instead.

[davidfowl]

Yes, see aspnet/Hosting#582 where I ran into this.

[JunTaoLuo]

I added the suggested enumeration as an extension method as part of aspnet/Hosting#596. Once it is implemented in Configuration, I'll remove the redundant extension in Hosting.

[divega]

@JunTaoLuo Yes I was looking at it this second. Thanks for the heads up.

@HaoK Let's have this as a public extension method in Configuration (it could live side-byside with the GetValue<T>() stuff). Need to decide about naming:

• 'ToKeyValuePairs()`
• Flatten()
• GetFlattenedSettings()

etc.

[HaoK]

I like IEnumerable<KeyValuePair<string, string>> Flatten(this IConfiguration configuration)

[HaoK]

@divega What GetValue stuff? The ones that live in the binder? or did you want me to move those to Configuration now as part of adding Flatten?

[divega]

I was referring to having this as an extension method in configuration alongside GetValue(), but this is a completely independent change.

I am not sure about the naming. Of the three options I wrote down I think Flatten is the one that is going to require looking into documentation the most in order to understand what it does, but I guess once you know what it does, it is the shortest 😄 Given that it is most likely not going to be a very commonly used API I would optimize for clarity.

[HaoK]

Well GetFlattenedSettings doesn't really make sense given the current config apis which don't use the term settings anywhere. I don't really think ToKeyValuePairs actually is very clear compared to something with the word Flatten in it.

Since this is just a DepthFirstTraversal, maybe that makes it clear?

DepthFirstEnumeration()
DepthFirstTraversal()

[HaoK]

Actually why can't we just call this Enumerate?

[divega]

I am not completely against any of these names besides probably the "depth first" ones, as I don't think the fact that is depth first is going to play much of a role 😄 Thinking of Enumerate() I also believe the existing LINQ idiom AsEnumerable() could work. The method would return an IEnumerable of KeyValuePair<string,string> which is a bit complicated but conceptually key value pairs is what the configuration is made of, so I don't think it would be going too far.

cc @shirhatti @danroth27

[MichaCo]

Well known terms (from linq) are ToList, ToArray, ToDictionary or AsEnumerable.
I'd use
ToDictionary returning IDictionary<string, string>), or
AsEnumerable returning IEnumerable<KeyValuePair<string, string>>

[HaoK]

I like AsEnumerable as well

[HaoK]

We could do both of those actually ToDictionary/AsEnumerable

[MichaCo]

👍

[divega]

Having AsEnumerable() is nice because unlike ToDictionary() it streams. Moreover once you have AsEnumerable() getting a dictionary is pretty easy using the existing LINQ operators:

var dictionary = configuration.AsEnumerable().ToDictionary(p => p.Key, x => p.Value);

So I don't think we would need to add ToDictionary().

[HaoK]

So why don't we just make IConfiguration extend IEumerable instead of adding an AsEnumerable?

[divega]

Mostly because it would automatically pollute our nice API with several dozen LINQ operators 😄 See my previous comment at #370 (comment).

[HaoK]

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