Question

Retargetable assembly references have been introduced for the .NET Compact Framework and are now used to support Portable Class Libraries.

Basically, the compiler emits the following MSIL:

.assembly extern retargetable mscorlib
{
    .publickeytoken = (7C EC 85 D7 BE A7 79 8E )                         
    .ver 2:0:5:0
}

How does the C# compiler understand it has to emit a retargetable reference, and how to force the C# compiler to emit such reference even outside of a portable class library?

Answer 1

For the assembly itself, it’s an assembly flag, ie [assembly: AssemblyFlags(AssemblyNameFlags.Retargetable)].

Make note that this flag is meaningless outside of platform assemblies – custom assemblies cannot be retargetable.

For references, it’s copied as part of the name from the assembly being referenced.