Configuration no-ops with no sources

[rynowak]

Setting a value in configuration with no sources has no effect. If this is by design then consider throwing instead of doing nothing.

var configuration = new Configuration();
configuration.Set("Hello", "World");

// Nope
configuration.Get("Hello")

[Eilon]

Hmm yeah maybe the default should have an in-memory config provider (that will barf if you commit?). I don't really like automatic defaults but I think here that might be the expectation...

[ChengTian]

@Eilon , a default in-memory config provider doesn't affect commit operation because in-memory config provider is not committable and we only write the last committable provider out.

The only problem of having default in-memory provider is that, when a user iterates all providers in a configuration object, he will see an provider not added by him. This can be addressed by adding explanation in documentation.

If you think it's Ok, I can take care of this issue.

[Eilon]

I think I'm OK with that, but @lodejard and @davidfowl should comment.

[lodejard]

I think you'd want the throwing to come from the Configuration rather than from a default ConfigurationSource... That is, Configuration methods would throw if there are no sources to handle that category of operation. Configuration.Set would throw if there are zero sources, Configuration.Commit would throw if there are no sources that implement commit... I guess that just leaves a choice - should .Get throw or return empty when there are zero sources? Could be either, but returning empty would be convenient if you wanted to pass an empty Configuration someplace that only called Get operations.

[davidfowl]

Get shouldn't throw ever (unless we're going to have a TryGet). I agree that the configuration itself should throw instead of the source

[ChengTian]

@davidfowl , we do have Configuration.TryGet().

By following @lodejard 's suggestion, a user cannot do Configuration.Set() when there is no source and the confusing scenario mentioned by @rynowak cannot happen. So I guess we can make empty Configuration return null when there is no source.

Then the only improvement I am going to make is that Configuration.Set() throws when there is no source.

[ardalis]

I see this issue is fixed in an upcoming release. Related question - is there a plan to ship a ConfigurationSource that is just an in-memory collection (sorry if I missed it somewhere)?
Disregard - found it. https://github.com/aspnet/Configuration/blob/dev/src/Microsoft.Framework.ConfigurationModel/Sources/MemoryConfigurationSource.cs