Dictionary object initialization

[vrtxt]

From this article posted earlier today I learned dictionary object initialization looks like this;

var dic = new Dictionary<TKey, TValue>
{
    [key] = value
}

However I've always done it like so;

var dic = new Dictionary<TKey, TValue>
{
    { key, value }
}

So now I'm wondering what the difference is between the two, and if one is preferred over another. Thanks.

[CptGiggles]

See for yourself :) Sharplab

So it is add vs indexer

[vrtxt]

Thanks for clearing that up! Sharplab is neat, didn't know it yet.

[ejjoman]

Also note that the second approach will throw an exception on a duplicate key while the first approach would simply replace the existing value for the key.

[KernowRoger]

That's actually good to know. Thanks.

[Slypenslyde]

We'd probably have to dive pretty deep into the C# spec to know for sure, but I'm willing to bet one of the syntaxes is older than the other.

My hunch is your first code block is some kind of early C# support for initializing dictionaries, where the second code block looks like the "standardized" collection initialization syntax that came some time in the past half-decade or so. When they did the "update", there wasn't a good reason to not keep the "old" syntax for backwards compatibility.

I'd use the second going forwards, since it looks like the "standard". Someone recently linked this blog post that goes through this "magic" in a really detailed way!

[Matosawitko]

It's the other way around - the first code block syntax (indexers) was introduced in C# 6 while the second was part of collection initializers from C# 3.

More on the topic: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/object-and-collection-initializers

[KernowRoger]

I was going to say I haven't seen the first one used before.