feat: Make it possible to "instance" SoLoud?

[filiph]

Description

SoLoud is currently always a singleton. There's a single SoLoud underlying engine, and the Dart API exposes it via SoLoud(). We could go that way but I wonder if it's possible (even easy?) to make SoLoud instanced.

This would mean that every time you call SoLoud(), you'd get a new instance of the engine. You could have multiple running at the same time.

PROs:

• Idiomatic way of configuring the engine. For example, we could have final engine = SoLoud(sampleRate: 44100);.
• Idiomatic way of passing the engine around. You create an instance, and then you provide it. This is in contrast with the current state, in which you can access the singleton instance via SoLoud() from anywhere. There is no way a controller/facade can "hide" SoLoud() from you via encapsulation.
• More robust testing. (One test cannot influence another.)
• Easier to avoid bugs such as https://github.com/alnitak/flutter_soloud/issues/31#issuecomment-1985672770, where one part of the app "forgets" to do something and there's a crash in another part of the app.

CONs:

• More work.
• A breaking change (even the example uses SoLoud() to access the same instance).

Requirements

• [ ] Verify that this is even something that the underlying (C++) engine supports
• [ ] Calls to SoLoud() create an instance that is independent from all other SoLoud() instances

[filiph]

Hey @alnitak, this will evidently need some thinking, but a first, relatively straightforward thing to answer would be:

Is SoLoud (the underlying C library) capable of being instanced?

If that's not the case, then we can clearly close this issue.

[alnitak]

Is SoLoud (the underlying C library) capable of being instanced?

I was thinking about this. Is not possible to have for example 2 SoLoud instances because there can be only one player instance on C side. But, yes, you can implement final engine = SoLoud(sampleRate: 44100); easily, but this engine will have that sampleRate for its entire life cycle. So I think we can close this.

[filiph]

Ok, this is really helpful. If it's not possible to have two instances on the C side, it shouldn't be possible to have two instances on the Dart side. This simplifies things. Thanks for the quick reply!