NightOwl888 opened a new issue, #1168:
URL: https://github.com/apache/lucenenet/issues/1168
### Is there an existing issue for this?
- [x] I have searched the existing issues
### Task description
We need to ensure that most of our `Dictionary<TKey, TValue>` usages
retrieve values using `TryGetValue()` instead of using indexer `var x =
dictionary[key]`. In Java, collections are designed not to throw exceptions
when entries don't exist. Since they always use refernece types, a check for
`null` is all that is required to determine if the key retrieval was successful.
However, generic .NET dictionaries allow the use of value types which may
not be nullable, which necessitates there be a `TryGetValue()` method to
determine whether an entry exists for a given key.
### Examples:
#### Value Types
```c#
float boost = m_boosts[m_fields[i]];
q.Boost = boost;
```
Becomes:
```c#
if (m_boosts.TryGetValue(m_fields[i], out float boost))
{
q.Boost = boost;
}
```
#### Reference Types
```c#
NumericDocValues instance = numericInstances.get(field.number);
if (instance == null) {
instance = loadNumeric(field);
numericInstances.put(field.number, instance);
}
return instance;
```
Becomes:
```c#
if (!numericInstances.TryGetValue(field.Number, out NumericDocValues
instance) || instance is null)
{
instance = LoadNumeric(field);
numericInstances[field.Number] = instance;
}
return instance;
```
> Note that for refernence types, we can eliminate the extra check for
`null` if the rest of the class is analyzed to ensure there can never be `null`
values in the dictionary.
We used a "squeaky wheel gets the grease" approach when fixing access to
`Dictionary<TKey, TValue>` calls. So, any gaps that the Lucene tests do not
cover have probably not yet been addressed.
> NOTE: .NET Generic dictionaries also implement non-generic interfaces.
When using these non-generic interfaces, the old "check for null" behavior is
still valid. So, in APIs where we are using `IDictionary` instead of
`IDictionary<TKey, TValue>`, we don't need to make these changes. These are
rare, though.
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