Code inspection: Parameter output value is always discarded (private accessibility)
Category: Redundancies in Symbol Declarations
ID: OutParameterValueIsAlwaysDiscarded.Local
EditorConfig: resharper_out_parameter_value_is_always_discarded_local_highlighting=[error|warning|suggestion|hint|none]
Language: C#, VB.NET
Requires SWA: No
tip
The C# 6.0 "out var" greatly reduces the amount of code needed to use methods with out
parameters — now we almost always declare variables inline and often use type inference to omit variable type: dictionary.TryGetValue(key, out var value).
Another aspect of out
parameters that C# 6.0 has improved is the ability to ignore the output parameter values that we don't need with M(out _)
or M(out var _)
syntax. So it's not uncommon to see invocations like DoSomething(arg, out _, out _)
in modern C# codebase.
JetBrains Rider analyzes such invocations and reports out
parameters that are discarded on all call sites. This helps identify potential problems of a value being always discarded and simplify the signature by removing the unused parameters.
Suboptimal code
class Test{ private Dictionary<string, int> _set = new(); // Parameter 'value' output value is always discarded private bool HasKey(string key, out int value) { return _set.TryGetValue(key, out value); } private void Usage(SetOfThings set) { if (set.HasKey("abc", out _)) Console.WriteLine("do something"); }}
After the quick-fix
class Test{ private Dictionary<string, int> _set = new(); private bool HasKey(string key) { int value; return _set.TryGetValue(key, out value); } private void Usage(SetOfThings set) { if (set.HasKey("abc")) Console.WriteLine("do something"); }}