Add a Config class to simplify adding configuration settings

The typical use is to inherit Config and add Setting<T> members:

  class MyClass : private Config
  {
    Setting<int> foo{this, 123, "foo", "the number of foos to use"};
    Setting<std::string> bar{this, "blabla", "bar", "the name of the bar"};

    MyClass() : Config(readConfigFile("/etc/my-app.conf"))
    {
      std::cout << foo << "\n"; // will print 123 unless overriden
    }
  };

Currently, this is used by Store and its subclasses for store
parameters. You now get a warning if you specify a non-existant store
parameter in a store URI.

1 files changed, 6 insertions, 6 deletions

diff --git a/src/libstore/s3-binary-cache-store.cc b/src/libstore/s3-binary-cache-store.cc
index 3053f908c4..2454552960 100644
--- a/src/libstore/s3-binary-cache-store.cc
+++ b/src/libstore/s3-binary-cache-store.cc
@@ -125,22 +125,22 @@ S3Helper::DownloadResult S3Helper::getObject(
 
 struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
 {
+    const Setting<std::string> region{this, Aws::Region::US_EAST_1, "region", {"aws-region"}};
+    const Setting<std::string> narinfoCompression{this, "", "narinfo-compression", "compression method for .narinfo files"};
+    const Setting<std::string> lsCompression{this, "", "ls-compression", "compression method for .ls files"};
+    const Setting<std::string> logCompression{this, "", "log-compression", "compression method for log/* files"};
+
     std::string bucketName;
 
     Stats stats;
 
     S3Helper s3Helper;
 
-    std::string narinfoCompression, lsCompression, logCompression;
-
     S3BinaryCacheStoreImpl(
         const Params & params, const std::string & bucketName)
         : S3BinaryCacheStore(params)
         , bucketName(bucketName)
-        , s3Helper(get(params, "aws-region", Aws::Region::US_EAST_1))
-        , narinfoCompression(get(params, "narinfo-compression", ""))
-        , lsCompression(get(params, "ls-compression", ""))
-        , logCompression(get(params, "log-compression", ""))
+        , s3Helper(region)
     {
         diskCache = getNarInfoDiskCache();
     }