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CA1854: Prefer the IDictionary.TryGetValue(TKey, out TValue) method

  • Article
Property Value
Rule ID CA1854
Title Prefer the IDictionary.TryGetValue(TKey, out TValue) method
Category Performance
Fix is breaking or non-breaking Non-breaking
Enabled by default in .NET 9 As suggestion

Cause

An IDictionary element access that's guarded by an IDictionary.ContainsKey check.

Rule description

When an element of an IDictionary is accessed, the indexer implementation checks for a null value by calling the IDictionary.ContainsKey method. If you also call IDictionary.ContainsKey in an if clause to guard a value lookup, two lookups are performed when only one is needed.

How to fix violations

Replace the IDictionary.ContainsKey invocation and element access with a call to the IDictionary.TryGetValue method.

Violation:

public string? GetValue(string key)
{
    if (_dictionary.ContainsKey(key))
    {
        return _dictionary[key];
    }

    return null;
}

Public Function GetValue(key As String) As String
    If _dictionary.ContainsKey(key) Then
        Return _dictionary(key)
    End If

    Return Nothing
End Function

Fix:

public string? GetValue(string key)
{
    if (_dictionary.TryGetValue(key, out string? value))
    {
        return value;
    }

    return null;
}

Public Function GetValue(key As String) As String
    Dim value as String

    If _dictionary.TryGetValue(key, value) Then
        Return value
    End If

    Return Nothing
End Function

When to suppress warnings

It's safe to suppress this warning if you're using a custom implementation of IDictionary that avoids a value lookup when performing the IDictionary.ContainsKey check.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable CA1854
// The code that's violating the rule is on this line.
#pragma warning restore CA1854

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.CA1854.severity = none

For more information, see How to suppress code analysis warnings.