Dictionary: upset-like usage [compact syntax]

Question

I would like to do something similar using some short syntax:

var p = new Dictionary<string, string>();
p["a"] = "2";
p["a"] = "3";

instead I have to do:

if (p.ContainsKey("a"))
    p["a"] = "2";
else
    p.Add("a", "2");

if (p.ContainsKey("a"))
    p["a"] = "3";
else
    p.Add("a", "3");

Does it exist a compact syntax?

You can do what you're trying to do... `p["a"] = "2";` is valid even if the key doesn't exist yet — Brian Kintz, Feb 21 '14 at 11:27
@elmugrat: sorry, you are right. Can you answer instead of commenting? I will accept it. The problem was that I didn't inizialized the dictionary. — Revious, Feb 21 '14 at 11:31
That's a *property bag", it has [been covered before](http://stackoverflow.com/questions/16131180/property-bag-for-c-sharp-class) — Hans Passant, Feb 21 '14 at 11:34
@HansPassant are you sure? Looks like he's just looking for help using a normal Dictionary... — Brian Kintz, Feb 21 '14 at 11:37
True, but I meant with general syntax as opposed to a specific application. I guess it doesn't matter though as long as he gets an answer — Brian Kintz, Feb 21 '14 at 11:41

Rudis · Answer 1 · 2014-02-21T11:33:28.463

9

By the MSDN for Item property:

If the specified key is not found, a get operation throws a KeyNotFoundException, and a set operation creates a new element with the specified key.

So compact syntax exists

edited Feb 21 '14 at 11:33

answered Feb 21 '14 at 11:30

Rudis

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score 3 · Accepted Answer · answered Feb 21 '14 at 11:32

3

p["a"] = "2";

is equivalent to

if (!p.ContainsKey("a"))
    p.Add("a", "2");
else
    p["a"] = "2";

The first should be preffered in fact, because it is performed faster.

answered Feb 21 '14 at 11:32

Athari

33,702
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score 1 · Answer 3 · answered Feb 21 '14 at 11:31

I have this extension method:

public static void AddOrKeep<K, V>(this IDictionary<K, V> dictionary, K key, V val)
{
    if (!dictionary.ContainsKey(key))
    {
        dictionary.Add(key, val);
    }
}

Use it like this:

dict.AddOrKeep("a", "2");

It keeps the current value if existent, but adds it if new.

score 0 · Answer 4 · answered Feb 21 '14 at 11:30

0

You can use ContainsKey Method of Dictionary to check whether particular Key contains by dictionary or not.

E.g.

if (!p.ContainsKey("a"))
{
p.Add("a","2");
}
else
{
p["a"] = "2";
}

answered Feb 21 '14 at 11:30

Jignesh Thakker

3,638
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Dictionary: upset-like usage [compact syntax]

4 Answers4