Any configuration that might differ across environments should be stored at the machine level, not the application level. (More info on configuration levels.)
These are the kinds of configuration elements that I typically store at the machine level:
When each environment (developer, integration, test, stage, live) has its own unique settings in the c:\Windows\Microsoft.NET\Framework64\v2.0.50727\CONFIG directory, then you can promote your application code between environments without any post-build modifications.
And obviously, the contents of the machine-level CONFIG directory get version-controlled in a different repository or a different folder structure from your app. You can make your .config files more source-control friendly through intelligent use of configSource.
I've been doing this for 7 years, on over 200 ASP.NET applications at 25+ different companies. (Not trying to brag, just want to let you know that I've never seen a situation where this approach doesn't work.)
The source referenced by the OP has some credibility ...but what about Microsoft - what is the stance on struct usage? I sought some extra learning from Microsoft, and here is what I found:
Consider defining a structure instead of a class if instances of the
type are small and commonly short-lived or are commonly embedded in
other objects.
Do not define a structure unless the type has all of the following characteristics:
- It logically represents a single value, similar to primitive types (integer, double, and so on).
- It has an instance size smaller than 16 bytes.
- It is immutable.
- It will not have to be boxed frequently.
Microsoft consistently violates those rules
Okay, #2 and #3 anyway. Our beloved dictionary has 2 internal structs:
[StructLayout(LayoutKind.Sequential)] // default for structs
private struct Entry //<Tkey, TValue>
{
// View code at *Reference Source
}
[Serializable, StructLayout(LayoutKind.Sequential)]
public struct Enumerator :
IEnumerator<KeyValuePair<TKey, TValue>>, IDisposable,
IDictionaryEnumerator, IEnumerator
{
// View code at *Reference Source
}
*Reference Source
The 'JonnyCantCode.com' source got 3 out of 4 - quite forgivable since #4 probably wouldn't be an issue. If you find yourself boxing a struct, rethink your architecture.
Let's look at why Microsoft would use these structs:
- Each struct,
Entry
and Enumerator
, represent single values.
- Speed
Entry
is never passed as a parameter outside of the Dictionary class. Further investigation shows that in order to satisfy implementation of IEnumerable, Dictionary uses the Enumerator
struct which it copies every time an enumerator is requested ...makes sense.
- Internal to the Dictionary class.
Enumerator
is public because Dictionary is enumerable and must have equal accessibility to the IEnumerator interface implementation - e.g. IEnumerator getter.
Update - In addition, realize that when a struct implements an interface - as Enumerator does - and is cast to that implemented type, the struct becomes a reference type and is moved to the heap. Internal to the Dictionary class, Enumerator is still a value type. However, as soon as a method calls GetEnumerator()
, a reference-type IEnumerator
is returned.
What we don't see here is any attempt or proof of requirement to keep structs immutable or maintaining an instance size of only 16 bytes or less:
- Nothing in the structs above is declared
readonly
- not immutable
- Size of these struct could be well over 16 bytes
Entry
has an undetermined lifetime (from Add()
, to Remove()
, Clear()
, or garbage collection);
And ...
4. Both structs store TKey and TValue, which we all know are quite capable of being reference types (added bonus info)
Hashed keys notwithstanding, dictionaries are fast in part because instancing a struct is quicker than a reference type. Here, I have a Dictionary<int, int>
that stores 300,000 random integers with sequentially incremented keys.
Capacity: 312874
MemSize: 2660827 bytes
Completed Resize: 5ms
Total time to fill: 889ms
Capacity: number of elements available before the internal array must be resized.
MemSize: determined by serializing the dictionary into a MemoryStream and getting a byte length (accurate enough for our purposes).
Completed Resize: the time it takes to resize the internal array from 150862 elements to 312874 elements. When you figure that each element is sequentially copied via Array.CopyTo()
, that ain't too shabby.
Total time to fill: admittedly skewed due to logging and an OnResize
event I added to the source; however, still impressive to fill 300k integers while resizing 15 times during the operation. Just out of curiosity, what would the total time to fill be if I already knew the capacity? 13ms
So, now, what if Entry
were a class? Would these times or metrics really differ that much?
Capacity: 312874
MemSize: 2660827 bytes
Completed Resize: 26ms
Total time to fill: 964ms
Obviously, the big difference is in resizing. Any difference if Dictionary is initialized with the Capacity? Not enough to be concerned with ... 12ms.
What happens is, because Entry
is a struct, it does not require initialization like a reference type. This is both the beauty and the bane of the value type. In order to use Entry
as a reference type, I had to insert the following code:
/*
* Added to satisfy initialization of entry elements --
* this is where the extra time is spent resizing the Entry array
* **/
for (int i = 0 ; i < prime ; i++)
{
destinationArray[i] = new Entry( );
}
/* *********************************************** */
The reason I had to initialize each array element of Entry
as a reference type can be found at MSDN: Structure Design. In short:
Do not provide a default constructor for a structure.
If a structure defines a default constructor, when arrays of the
structure are created, the common language runtime automatically
executes the default constructor on each array element.
Some compilers, such as the C# compiler, do not allow structures to
have default constructors.
It is actually quite simple and we will borrow from Asimov's Three Laws of Robotics:
- The struct must be safe to use
- The struct must perform its function efficiently, unless this would violate rule #1
- The struct must remain intact during its use unless its destruction is required to satisfy rule #1
...what do we take away from this: in short, be responsible with the use of value types. They are quick and efficient, but have the ability to cause many unexpected behaviors if not properly maintained (i.e. unintentional copies).
Best Answer
You're working against the architecture of app.config. You get one app.config file per executable (EXE, not DLL). The executable launches, creates its AppDomain, and then loads MyApp.exe.config. You can add app.config objects all you want in Visual Studio, but they are ignored for DLLs. I think what you want to do is manually copy the XML from the dll.config and paste it into the application level app.config. (I'm sure there's a way to automate this using TeamBuild or some such.) The overridden values will then be available to your Properties.Settings class.