.Net程序集映射策略的目的

Question

what is the reason/purpose for doing assembly mapping? changing version policy?. I understand that if your app.exe wanted to use a new assembly version you could redirect assembly version, but why would you want to?. Wouldn't the new version of dependent assembly change?

Suppose there is a calc.dll and app.exe. app.exe depends on calc.dll. If calc.dll was rebuild and bunch of methods renamed wouldn't app.exe fail when ran when redirected to calc.dll new version?

Answer 1

Since authors that care about customers strive to keep interfaces/types of the same assembly backward-compatible then using newer versions of the same assembly is generally not a problem.

Main issue is other assemblies depending on older versions.

Lets say there is common "Shared.dll" which has multiple compatible versions (well known sample - JSON.Net) and used by your code as well by some other DLL your code needs:

ThridParty.dll (v1) -> Shared.dll (v1)
YourApp.exe -> Shared.dll (latest = v5), ThirdParty.dll (v1)

Now you need 2 versions of Shared.dll but both have same file name (solvable by manually loading one) and inability to use objects produces by mixed versions (Shared.Type1 from v1 is not the same as Shared.Type1 from v5 by .Net rules).

To solve you use assembly redirect and say "whenever anyone asks for Shared.dll v1 use Shared.dll v5". This way ThridParty.dll continue to work just fine and you no longer face problems with 2 files/versions loaded at the same time.