Document CStruct vs CStructEntity about fiddle

[kou]

I don't understand the real reason for CStruct and CStructEntity because I'm not the create of CStruct.
But I think that the creator wants to avoid class CUnion < CStruct inheritance.

They exist for backward compatibility of DL (ruby-dl2): https://github.com/ruby/ruby/blob/ruby_2_1/ext/dl/lib/dl/struct.rb

ruby-dl uses Struct and Union directly and class Union < Struct: https://github.com/ruby/ruby/blob/ruby_1_8_7/ext/dl/lib/dl/struct.rb

Anyway, we'll be able to improve them with keeping backward compatibility.

Normal users will use Fiddle::Importer.struct instead of using Fiddle::CStructBuilder.create directly.

[kou]

Ah, I got it. The creator wants to hide implementation details.

[chrisseaton]

The problem is that these terms are super vague. 'entity'? That could mean anything or nothing. Here, an 'entity' is really a pointer to an instance of a type.

And CStruct is really a sort of factory... an object that supplies something used in a constructor. It could be a symbol like :struct instead.

[kou]

What do you want to do in this issue?
Do you want to add more documents?
Do you want to reconstruct lib/fiddle/struct.rb?

[chrisseaton]

I think I've clarified this in #41.

[kou]

OK.
I close this.