Catalog / Primitives / inline-field

Inline Field

Replaces every read of a field that is only ever assigned by its initialiser with that initialiser, across the solution, and removes the field.

Precondition

The field has an initialiser.
Nothing assigns the field, increments it or passes it by ref or out, including constructors.
Evaluating the initialiser again at each use gives the same value with no side effects: it is built from constants, literals, default, typeof, static readonly or constant fields, and built-in operators and casts. An initialiser that creates an object or calls a method is refused, because each use would get a new object or a new call.
No use of the field is inside nameof.

Transformation

Each read, including this._field and Type.Field, is replaced by the initialiser, qualified and parenthesised as the use needs, as Inline Constant does.
The field is removed with its comments, and the blank lines around it close up. A field declared alongside others is removed from the declaration only.

Preserved

Every value the code reads, given the precondition.
Nullable annotations on the code that used the field.

Limitations

A static readonly field read from another static initialiser of its own type could observe the field before it was initialised; inlining gives the initialised value instead.
Code outside the solution that uses a public field is not updated.

Error codes

Code	Meaning
`no-initializer`	the field has no initialiser
`written-after-initialization`	the field is assigned somewhere other than its initialiser
`initializer-not-inlinable`	the initialiser could give a different value or have side effects when evaluated again
`used-in-nameof`	a use of the field is inside `nameof`

Cases

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

#across-files

A static readonly field used from another file is inlined there too, with names in its value qualified for the new location

success

Targetsymbol F:Shop.Rates.Standard

Invoice.csmodified

Rates.csmodified

View fixture on GitHub

#initializer-not-inlinable-rejected

Refuses a field whose initialiser creates an object or calls a method, since each use would get a new value

refusal

Targetsymbol F:Shop.Basket._items

Refusesinitializer-not-inlinable; every file is left unchanged

Basket.csinput

View fixture on GitHub

#no-initializer-rejected

Refuses a field that has no initialiser to inline

refusal

Targetsymbol F:Shop.Counter._step

Refusesno-initializer; every file is left unchanged

Counter.csinput

View fixture on GitHub

#nullable-reference

A field declared nullable is replaced by its value, and the code keeps its nullable annotations

success

Targetsymbol F:Shop.Profile._fallback

Projectnullable enable

Profile.csmodified

View fixture on GitHub

#parenthesises-value

The value is parenthesised where the use binds more tightly than the initialiser

success

Targetsymbol F:Shop.Pricing._markup

Pricing.csmodified

View fixture on GitHub

#simple

Replaces every read of a field assigned only by its initialiser with the initialiser, and removes the field

success

Targetsymbol F:Shop.Greeter._greeting

Greeter.csmodified

View fixture on GitHub

#written-after-initialization-rejected

Refuses a field that is assigned somewhere other than its initialiser

refusal

Targetsymbol F:Shop.Counter._step

Refuseswritten-after-initialization; every file is left unchanged

Counter.csinput

View fixture on GitHub

1	1		namespace Shop
2	2		{
3	3		public class Invoice
4	4		{
5		−	public decimal Gross(decimal net) => net + net * Rates.Standard;
	5	+	public decimal Gross(decimal net) => net + net * Rates.Vat;
6	6		}
7	7		}

1	1		namespace Shop
2	2		{
3	3		public static class Rates
4	4		{
5	5		public const decimal Vat = 0.2m;
6	6
7		−	// The rate most goods pay.
8		−	public static readonly decimal Standard = Vat;
9		−
10		−	public static decimal Tax(decimal net) => net * Standard;
	7	+	public static decimal Tax(decimal net) => net * Vat;
11	8		}
12	9		}

1		using System.Collections.Generic;
2
3		namespace Shop
4		{
5		public class Basket
6		{
7		private readonly List<string> _items = new List<string>();
8
9		public void Add(string item) => _items.Add(item);
10
11		public int Count => _items.Count;
12		}
13		}

1		namespace Shop
2		{
3		public class Counter
4		{
5		private readonly int _step;
6
7		public Counter(int step)
8		{
9		_step = step;
10		}
11
12		public int Next(int value) => value + _step;
13		}
14		}

1	1		namespace Shop
2	2		{
3	3		public class Profile
4	4		{
5		−	private readonly string? _fallback = "anonymous";
6		−
7		−	public string? Display(string? name) => name ?? _fallback;
	5	+	public string? Display(string? name) => name ?? "anonymous";
8	6		}
9	7		}

1	1		namespace Shop
2	2		{
3	3		public class Pricing
4	4		{
5		−	private readonly decimal _markup = 1m + 0.2m;
	5	+	public decimal Price(decimal cost) => cost * (1m + 0.2m);
6	6
7		−	public decimal Price(decimal cost) => cost * _markup;
8		−
9		−	public decimal Margin(decimal cost) => cost * _markup - cost;
	7	+	public decimal Margin(decimal cost) => cost * (1m + 0.2m) - cost;
10	8		}
11	9		}

1	1		namespace Shop
2	2		{
3	3		public class Greeter
4	4		{
5		−	private readonly string _greeting = "Hello";
6	5		private int _count;
7	6
8	7		public string Greet(string name)
9	8		{
10	9		_count++;
11		−	return this._greeting + ", " + name;
	10	+	return "Hello" + ", " + name;
12	11		}
13	12
14	13		public int Count => _count;
15	14
16		−	public bool IsGreeting(string text) => text == _greeting;
	15	+	public bool IsGreeting(string text) => text == "Hello";
17	16		}
18	17		}

1		namespace Shop
2		{
3		public class Counter
4		{
5		private int _step = 1;
6
7		public void Faster() => _step = 2;
8
9		public int Next(int value) => value + _step;
10		}
11		}