This part of the C# idioms series is only about dictionaries.
Instead of checking if a dictionary contains an item before adding it, use TryAdd
TryAdd
will return if an item was added or not to the dictionary. Unlike Add
, if the given key is already in the dictionary, TryAdd
won't throw any exception. It will simply do nothing. The item is already there.
Before,
var myDictionary = new Dictionary<string, string>();
myDictionary.Add("foo", "bar");
// System.ArgumentException: An item with the same key has already been added. Key: foo
myDictionary.Add("foo", "baz");
After,
var myDictionary = new Dictionary<string, string>();
if (!myDictionary.ContainsKey("foo"))
myDictionary.Add("foo", "bar");
Even better,
var myDictionary = new Dictionary<string, string>();
myDictionary.TryAdd("foo", "bar"); // true
myDictionary.Add("foo", "baz");
myDictionary.TryAdd("foo", "bar"); // false
Avoid KeyNotFoundException
with TryGetValue
or GetValueOrDefault
At least now, the KeyNotFoundException
message contains the name of the not-found key. The old days chasing the not-found key are over.
On one hand, TryGetValue
uses an output parameter with the found value. It outputs a default value when the dictionary doesn't contain the item. TryGetValue
dates back to the days without tuples.
On another hand, GetValueOrDefault
returns a default value or one you provide if the key wasn't found.
Before,
var dict = new Dictionary<string, string>();
// System.Collections.Generic.KeyNotFoundException: The given key 'foo' was not present in the dictionary.
dict["foo"];
After,
var dict = new Dictionary<string, string>();
dict.TryGetValue("foo", out var foo); // false, foo -> null
dict.Add("foo", "bar");
dict.TryGetValue("foo", out foo); // true, foo -> "bar"
Even better,
var dict = new Dictionary<string, string>();
dict.GetValueOrDefault("foo"); // null
dict.GetValueOrDefault("foo", "withoutFoo"); // "withoutFoo"
dict.Add("foo", "bar");
dict.GetValueOrDefault("foo", "withoutFoo"); // "bar"
Happy coding!
Top comments (1)
haha, great