anchor.diff:  { stdenv
   , fetchurl
  -, requireFile
   , autoPatchelfHook
   , fixDarwinDylibNames
   , unzip
  
positive.code:     x86_64-darwin = "macos.x64";
    }.${stdenv.hostPlatform.system} or throwSystem;
  
    # calculate the filename of a single zip file
    srcFilename = component: arch: version: rel:
      "instantclient-${component}-${arch}-${version}" +
      (optionalString (rel != "") "-${rel}") +
      (optionalString (arch == "linux.x64") "dbru") + # ¯\_(ツ)_/¯
      ".zip";
  
    # fetcher for the clickthrough artifacts (requiring manual download)
    fetchClickThrough =  srcFilename: hash: (requireFile {
      name = srcFilename;
      url = "https://www.oracle.com/database/technologies/instant-client/downloads.html";
      sha256 = hash;
    });
  
    # fetcher for the non clickthrough artifacts
    fetchSimple = srcFilename: hash: fetchurl {
      url = "https://download.oracle.com/otn_software/linux/instantclient/193000/${srcFilename}";
      sha256 = hash;
    };
  
    # pick the appropriate fetcher depending on the platform
    fetcher = if stdenv.hostPlatform.system == "x86_64-linux" then fetchSimple else fetchClickThrough;
  
    # assemble srcs
    srcs = map (component:
  
negative.code:       odbc    = "1g1z6pdn76dp440fh49pm8ijfgjazx4cvxdi665fsr62h62xkvch";
      };
      x86_64-darwin = {
        basic   = "f4335c1d53e8188a3a8cdfb97494ff87c4d0f481309284cf086dc64080a60abd";
        sdk     = "b46b4b87af593f7cfe447cfb903d1ae5073cec34049143ad8cdc9f3e78b23b27";
        sqlplus = "f7565c3cbf898b0a7953fbb0017c5edd9d11d1863781588b7caf3a69937a2e9e";
        odbc    = "f91da40684abaa866aa059eb26b1322f2d527670a1937d678404c991eadeb725";
      };
    }.${stdenv.hostPlatform.system} or throwSystem;
  
    # rels per component and architecture, optional
    rels = {
    }.${stdenv.hostPlatform.system} or {};
  
    # convert platform to oracle architecture names
  