Construct a static lookup

Question

Say I have a giant list of definitions that are used to lookup values that an object can default to given a "type number". This type number is unique, and points to data that the object will be set to when initialized with it.

My usual go-to is to have a static property that will return a new Dictionary with each get. E.g.

public static Dictionary<long, Tuple<string,DefaultValue>> Defaults
{
   get { return new Dictionary<long, DefaultValue>() 
         {
            { 123, new DefaultValue("Name of default 1", 12312, 23544, ...)},
            { 456, new DefaultValue("Name of default 2", 36734, 74367, ...)},
            ... 
         }
   }
}

This works, and the lookup list will likely never be large enough for this to noticeably impact performance or memory usage, but being somewhat stingy on performance I don't like the idea of having a new Dictionary instantiated every time it is referenced. I would much rather it be completely hard-coded into memory.

How would this be solved in a professional way? I feel like the way I am doing it above is incredibly sloppy.

Even when the getter uses `return new Dictionary<>(){ ... }` in the getter? I forgot to include that in the OP — w0f, Jul 05 '17 at 15:55

Igor · Accepted Answer · 2017-07-05T16:06:34.393

You can use an auto-property initializer or set the value in the static constructor. The latter is shown below.

static MyClass()
{
   Defaults = new Dictionary<long, DefaultValue>(){
        { 123, new DefaultValue("Name of default 1", 12312, 23544, ...)},
        { 456, new DefaultValue("Name of default 2", 36734, 74367, ...)},
      };
}

public static Dictionary<long, DefaultValue> Defaults {get; private set;}

Example with Auto-property initializer (no static constructor is needed and the private set is omitted as the assumption can now be made you are using a c# version that supports that).

public static Dictionary<long, DefaultValue> Defaults {get;} = new Dictionary<long, DefaultValue>(){
        { 123, new DefaultValue("Name of default 1", 12312, 23544, ...)},
        { 456, new DefaultValue("Name of default 2", 36734, 74367, ...)},
      };

Side note: If the values should not be altered you could also expose the IReadonlyDictionary interface on the property.

Shouldn't that be `Defaults = new Dictionary<...> ...`? – Peter B Jul 05 '17 at 15:56 — Peter B, Jul 05 '17 at 15:56
@PeterB - shoot, I did forget the `new` keyword. Thank you. – Igor Jul 05 '17 at 15:56 — Igor, Jul 05 '17 at 15:56
Couldn't a `Lazy>` be an option either? – Icepickle Jul 05 '17 at 16:17 — Icepickle, Jul 05 '17 at 16:17

score 0 · Answer 2 · answered Jul 05 '17 at 16:13

If the lookup table is small and your goal is to increase the performance of the lookup operation then you can also consider using a function with a switch statement instead of a lookup dictionary.

See this answer for more information: https://stackoverflow.com/a/11617459/1709981

Construct a static lookup

2 Answers2