Exploring the GAC with F# and Mono.Cecil

Mono.Cecil can be used to look inside assemblies. May be you want to search GAC to find types that implement a certain interface. In this post, I’ll show how to find all the types that implement IDisposable as an example.

The output of this code on my machine:

There are 1620 DLLs in C:\Windows\assembly.
There are 365 DLLs in C:\Windows\Microsoft.NET\assembly.
# of public types: 30071
# IDisposable: 733

The code:

open System

open System.IO

open Mono.Cecil

let windir = Environment.GetFolderPath Environment.SpecialFolder.Windows

let pathGac2 = Path.Combine(windir, "assembly")

let pathGac4 = Path.Combine(windir, @"Microsoft.NET\assembly")

let main() =

  let dlls2 = Directory.EnumerateFiles(pathGac2, "*.dll", SearchOption.AllDirectories)

  let dlls4 = Directory.EnumerateFiles(pathGac4, "*.dll", SearchOption.AllDirectories)

  printfn "There are %d DLLs in %s." (Seq.length dlls2) pathGac2

  printfn "There are %d DLLs in %s." (Seq.length dlls4) pathGac4

  let readModule (dll:string) = ModuleDefinition.ReadModule dll

  let publicTypes =

    dlls4

    |> Seq.map readModule

    |> Seq.map (fun m -> m.Types)

    |> Seq.concat

    |> Seq.filter (fun t -> t.IsPublic)

  // How many public types in all .NET 4 assemblies?

  publicTypes |> Seq.length |> printfn "# of public types: %d"

  // How many of those implement the IDisposable interface?

  let isFullNameEqual (t:Type) (tr:TypeReference) = t.FullName = tr.FullName

  publicTypes

  |> Seq.filter (fun t -> t.Interfaces |> Seq.exists (isFullNameEqual typeof<IDisposable>))

  |> Seq.length |> printfn "# IDisposable: %d"

  ()

main()

A source release of the latest version of Mono.Cecil can be downloaded here. I built 0.9.3 for .NET 4 Client Profile in the Release configuration without issue.