How do I add a Python-style Get() method which takes a default value to my C# dictionaries?

Question

I'd like to be able to specify a default value to return if the key I specify can't be found in the dictionary.

e.g.

int default = 5;
string key = "MyKey";
int foo = myDictionary.GetValue(key, default);

if key is in myDictionary foo should hold the value from the dictionary, otherwise it will hold 5.

Answer 1

I found a piece of code here which does the job nicely by adding an extension method to IDictionary:

using System.Collections.Generic;

namespace MyNamespace {
    public static class DictionaryExtensions {
        public static V GetValue<K, V>(this IDictionary<K, V> dict, K key) {
            return dict.GetValue(key, default(V));
        }

        public static V GetValue<K, V>(this IDictionary<K, V> dict, K key, V defaultValue) {
            V value;
            return dict.TryGetValue(key, out value) ? value : defaultValue;
        }
    }
}

Answer 2

The best way is to use TryGetValue, a possible way is by doing:

    int default = 5;
    string key = "MyKey"; 
    int foo = 0;
    defaultValue = 5;
    (myDictionary.TryGetValue(key, out foo))?return foo: return defaultValue;

If you try to get a value that is not present the TryGetValue returns false, which means that your use the second part of the clause.

You can also decide to set foo to you default value, use the TryGetValue and return foo in any case.