add DeliveryModes convenience enum

[Jalalx]

Proposed Changes

This pull request adds the DeliveryModes convenience class as a helper to prevent developers from hardcoding delivery mode codes using magic numbers.

Types of Changes

What types of changes does your code introduce to this project?

• Bug fix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

[michaelklishin]

Thank you. Besides a bit of work on naming, this looks like a good addition to me.

[Matthew-Davey]

How about an enum?

public enum DeliveryMode : byte
{
    Transient = 1,
    Persistent = 2
}

[michaelklishin]

I like @Matthew-Davey's idea. @Jalalx WDYT about using an enum?

[Jalalx]

Using an enum was my initial idea, but then two options should be considered:

1. Changing IBasicProperties.DeliveryMode from byte to DeliveryModes enum, which introduces a breaking change to user code and touches too many areas.
2. Leaving IBasicProperties.DeliveryMode as is and just add the new DeliveryModes enum so user can use it. But then, developer should explicitly convert enum values to bytes (personally, I found it annoying 😕).

   public enum DeliveryModes: byte {  Transient = 1, Persistent = 2 };
   // ...
   
   IBasicProperties props = ... // 
   
   // error CS0266: Cannot implicitly convert type 'DeliveryModes' to 'byte'. An explicit conversion exists (are you missing a cast?)
   props.DeliveryMode = DeliveryModes.Transient
   // You have to explicitly convert enum value to byte like this:
   props.DeliveryMode = (byte)DeliveryModes.Transient

That's why I considered going with simple const values in a static DeliveryModes class.

Please let me know what you think.

[bollhals]

I'd agree with the above statement of @Jalalx .

On the other hand I'm not sure how the usage is divided between the DeliveryMode and the Persistent property. I've personally never used the DeliveryMode. So the benefit for me would be 0.

[Jalalx]

Yes, but I wasn't aware of that property until I see that reference while making this PR 😅 I guess DeliveryMode is there for backward compatibility because removing it would introduce unnecessary breaking changes to existing client code.

[sungam3r]

Changing IBasicProperties.DeliveryMode from byte to DeliveryModes enum, which introduces a breaking change to user code and touches too many areas.

But it's acceptable for the next major version. See #1056

[Jalalx]

@sungam3r Does it worth a breaking change? What do you think @michaelklishin?

[bollhals]

@sungam3r Does it worth a breaking change? What do you think @michaelklishin?

It's not breaking, it's just adding another public class.

Edit: whooops, didn't read the whole comment section, my bad. disregard my comment.

[sungam3r]

Does it worth a breaking change?

Why not if v7 is on the way? Nobody likes magic numbers.

[Jalalx]

So, should I drop the DeliveryModes class and introduce a DeliveryModes enum? Is everybody agree on this?

[lukebakken]

Thank you @Jalalx