Retrieving Dictionary Value Best Practices

Well in fact TryGetValue is faster. How much faster? It depends on the dataset at hand. When you call the Contains method, Dictionary does an internal search to find its index. If it returns true, you need another index search to get the actual value. When you use TryGetValue, it searches only once for the index and if found, it assigns the value to your variable.

Edit:

Ok, I understand your confusion so let me elaborate:

Case 1:

if (myDict.Contains(someKey))
     someVal = myDict[someKey];

In this case there are 2 calls to FindEntry, one to check if the key exists and one to retrieve it

Case 2:

myDict.TryGetValue(somekey, out someVal)

In this case there is only one call to FindKey because the resulting index is kept for the actual retrieval in the same method.

TryGetValue is slightly faster, because FindEntry will only be called once.

How much faster? It depends on the dataset at hand. When you call the Contains method, Dictionary does an internal search to find its index. If it returns true, you need another index search to get the actual value. When you use TryGetValue, it searches only once for the index and if found, it assigns the value to your variable.

FYI: It's not actually catching an error.

It's calling:

public bool TryGetValue(TKey key, out TValue value)
{
    int index = this.FindEntry(key);
    if (index >= 0)
    {
        value = this.entries[index].value;
        return true;
    }
    value = default(TValue);
    return false;
}

ContainsKey is this:

public bool ContainsKey(TKey key)
{
    return (this.FindEntry(key) >= 0);
}