Catalog / Primitives / safe-delete-local

Safe Delete Local

Deletes a local variable that nothing uses, keeping whatever its initializer did beyond producing a value.

Precondition

The caret is on a local declared by a local declaration statement.
Nothing reads or assigns the local after its declaration.
The local is not a using declaration, whose disposal at the end of the scope is behaviour.

Transformation

A declaration whose initializer has no side effects is removed. Comments above it stay, above the statement that follows.
An initializer with side effects, one that calls a method, creates an object, assigns, awaits or indexes, is kept:
as a statement of its own when C# allows one, so var loaded = Load(); becomes Load();;
otherwise as a discard, so var total = Load() + 1; becomes _ = Load() + 1;.
A local declared alongside others loses just its declarator. When its initializer is kept, the declaration is split around it so every initializer still runs in the order written: int first = Next(), second = Next(), third = Next(); becomes three statements.

Preserved

The order and number of evaluations of every initializer.
Comments above the declaration.

Limitations

Property reads are treated as free of side effects, so var count = list.Count; is removed outright.
A local that is only written, never read, is refused rather than deleted with its assignments.
Locals declared by for, foreach, using statements, patterns and out arguments are not offered.

Error codes

Code	Meaning
`local-referenced`	the local is read or assigned after its declaration
`using-declaration`	the local is a `using` declaration
`not-a-local`	the caret is not on a local variable

Cases

Diffs show each file from before to after. /*[*/ … /*]*/ marks a selection and /*^*/ a caret; the runner removes them before the refactoring runs.

#assigned-later-refused

Refuses to delete a local that is assigned after its declaration

refusal

TargetSample.cs, the /*^*/ caret

Refuseslocal-referenced; every file is left unchanged

Sample.csinput

View fixture on GitHub

#call-initializer-kept

Keeps a call that initialised the deleted local as a statement, with the comment above it

success

TargetSample.cs, the /*^*/ caret

Sample.csmodified

View fixture on GitHub

#expression-initializer-discarded

Keeps an initializer with side effects that is not a statement on its own as a discard assignment

success

TargetSample.cs, the /*^*/ caret

Sample.csmodified

View fixture on GitHub

#local-referenced-refused

Refuses to delete a local that is read

refusal

TargetSample.cs, the /*^*/ caret

Refuseslocal-referenced; every file is left unchanged

Sample.csinput

View fixture on GitHub

#not-a-local-refused

Refuses when the caret is on a parameter rather than a local

refusal

TargetSample.cs, the /*^*/ caret

Refusesnot-a-local; every file is left unchanged

Sample.csinput

View fixture on GitHub

#nullable-local

Deletes an unused nullable local, keeping the lookup that initialised it

success

TargetSample.cs, the /*^*/ caret

Projectnullable enable

Sample.csmodified

View fixture on GitHub

#one-of-several-declarators

Deletes one local from a declaration of several, keeping its call between the others in order

success

TargetSample.cs, the /*^*/ caret

Sample.csmodified

View fixture on GitHub

#unused-local

Deletes a local that is never read, whose initializer has no side effects

success

TargetSample.cs, the /*^*/ caret

Sample.csmodified

View fixture on GitHub

#using-declaration-refused

Refuses to delete a using declaration, whose disposal is behaviour

refusal

TargetSample.cs, the /*^*/ caret

Refusesusing-declaration; every file is left unchanged

Sample.csinput

View fixture on GitHub

1		public class Sample
2		{
3		public void Run(int a)
4		{
5		var /^/last = 0;
6		last = a;
7		}
8		}

1	1		public class Sample
2	2		{
3	3		private int _loads;
4	4
5	5		public int Run()
6	6		{
7	7		// Warm the cache.
8		−	int /^/loaded = Load();
	8	+	Load();
9	9
10	10		return _loads;
11	11		}
12	12
13	13		private int Load() => ++_loads;
14	14		}

1	1		public class Sample
2	2		{
3	3		private int _loads;
4	4
5	5		public int Run()
6	6		{
7		−	var /^/total = Load() + 1;
	7	+	_ = Load() + 1;
8	8		return _loads;
9	9		}
10	10
11	11		private int Load() => ++_loads;
12	12		}

1		public class Sample
2		{
3		public int Sum(int a, int b)
4		{
5		var /^/total = a + b;
6		return total;
7		}
8		}

1	1		using System.Collections.Generic;
2	2
3	3		public class Sample
4	4		{
5	5		private readonly Dictionary<string, string> _names = new Dictionary<string, string>();
6	6
7	7		public int Count(string key)
8	8		{
9		−	string? /^/name = Find(key);
	9	+	Find(key);
10	10		return _names.Count;
11	11		}
12	12
13	13		private string? Find(string key) => _names.TryGetValue(key, out var value) ? value : null;
14	14		}

1		public class Sample
2		{
3		public int Twice(int /^/value) => 2;
4		}

1	1		public class Sample
2	2		{
3	3		private int _next;
4	4
5	5		public int Run()
6	6		{
7		−	int first = Next(), /^/second = Next(), third = Next();
	7	+	int first = Next();
	8	+	Next();
	9	+	int third = Next();
8	10		return first + third;
9	11		}
10	12
11	13		private int Next() => ++_next;
12	14		}

1	1		public class Sample
2	2		{
3	3		public int Sum(int a, int b)
4	4		{
5		−	var /^/doubled = a * 2;
6	5		return a + b;
7	6		}
8	7		}

1		using System.IO;
2
3		public class Sample
4		{
5		public void Run()
6		{
7		using var /^/stream = new MemoryStream();
8		}
9		}