What rules govern cross-version compatibility for .NET applications and the C# language?
- by John Feminella
For some reason I've always had trouble remembering the backwards/forwards compatibility guarantees made by the framework, so I'd like to put that to bed forever.
Suppose I have two assemblies, A and B. A is older and references .NET 2.0 assemblies; B references .NET 3.5 assemblies. I have the source for A and B, Ax and Bx, respectively; they are written in C# at the 2.0 and 3.0 language levels. (That is, Ax uses no features that were introduced later than C# 2.0; likewise Bx uses no features that were introduced later than 3.0.)
I have two environments, C and D. C has the .NET 2.0 framework installed; D has the .NET 3.5 framework installed.
Now, which of the following can/can't I do?
Running:
run A on C? run A on D?
run B on C? run C on D?
Compiling:
compile Ax on C? compile Ax on D?
compile Bx on C? compile Bx on D?
Rewriting:
rewrite Ax to use features from the C# 3 language level, and compile it on D, while having it still work on C?
rewrite Bx to use features from the C# 4 language level on another environment E that has .NET 4, while having it still work on D?'
Referencing from another assembly:
reference B from A and have a client app on C use it?
reference B from A and have a client app on D use it?
reference A from B and have a client app on C use it?
reference A from B and have a client app on D use it?
More importantly, what rules govern the truth or falsity of these hypothetical scenarios?
