The Contract Reference Assembly is a special kind of assembly which preserves any code contracts you defined in your source code files. This is necessary because at compile-time, the code contracts’ “rewriter” (ccrewriter) removes or replaces each contract with equivalent verification code (Contract.Requires(someBool) might be rewritten as if (!someBool) throw).
Without the code contracts, if you later reference the compiled assembly (not the project and all it’s source code files) in a different solution, it may not be aware of any of the code contracts. Had a Contract Reference Assembly been created, the IDE could take into account any contracts in that assembly during static analysis.
As for the settings, here’s what they mean:
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(none)means you have not made a selection, and so no reference assembly will be created. If another assembly depends on this one and you have selectedBuildfor it, you may receive an error/warning that “no contract reference assembly was found.” -
If you change the setting to
Build, a reference assembly will be created that contains all of your contracts. You will be able to use all of the code contracts defined in that assembly as if you had the source code. Choose this if you are creating a library that will be used by a 3rd party (a NuGet package, for example) or anyone after the assembly is compiled so they will have the benefit of your code contracts in static analysis. -
If you change the setting to
DoNotBuild, no reference assembly will be built preserving your code contracts. Choose this if you don’t intend for this assembly to be used anywhere else, or if all other users of the assembly will have access to the source code and not need the reference assembly. It may speed up the build a little.