Catalog / Primitives / convert-extension-method-to-static

Convert Extension Method to Static Method

The reverse of Convert to Extension Method: an extension method becomes an ordinary static method, and every extension-style call becomes a static call.

Arguments

Argument	Meaning
`target.symbol`	the extension method, such as `M:Shop.Text.Shout(System.String)`

Precondition

The method is an extension method.
No call uses it through null-conditional access (value?.Shout()), whose static form would need a null check.
It is not used as a method group on a value (value.Shout passed as a delegate), which has no static equivalent.

Transformation

this is removed from the first parameter.
Each call value.Shout(...) becomes Text.Shout(value, ...), with the receiver as the first argument. The class name is as short as the calling file allows, and a call inside the class is left unqualified.
Chained calls convert together: raw.Trimmed().ToUpperInvariant() becomes Formatting.Trimmed(raw).ToUpperInvariant().
Explicit type arguments are kept.
Calls already written in static form are unchanged.

Preserved

The behaviour of every call, including evaluation order: the receiver is evaluated first, as the first argument.

Limitations

LINQ query syntax that binds to the method (a Select or Where extension) is not rewritten, and stops compiling.

Error codes

Code	Meaning
`not-extension`	the method is not an extension method
`conditional-access`	a call uses null-conditional access
`method-group`	the method is used as a method group on a value

Cases

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

#conditional-call-rejected

Refuses while a null-conditional call uses the extension, since the static form would change when it runs

refusal

Targetsymbol M:Shop.Text.Shout(System.String)

Refusesconditional-access; every file is left unchanged

Text.csinput

View fixture on GitHub

#generic

A generic extension method keeps its explicit type arguments at call sites

success

Targetsymbol M:Shop.Sequences.FirstOr``1(System.Collections.Generic.IEnumerable{``0},``0)

Basket.csmodified

Sequences.csmodified

View fixture on GitHub

#not-extension-rejected

Refuses a method that is not an extension method

refusal

Targetsymbol M:Shop.Text.Shout(System.String)

Refusesnot-extension; every file is left unchanged

Text.csinput

View fixture on GitHub

#other-namespace

Calls from a namespace that imports the extension's namespace name the class simply; chained calls keep their order

success

Targetsymbol M:Shop.Text.Formatting.Trimmed(System.String)

Formatting.csmodified

Report.csmodified

View fixture on GitHub

#simple

Drops this from an extension method, and extension calls in other files become static calls on its class

success

Targetsymbol M:Shop.Text.Shout(System.String)

Checkout.csmodified

Text.csmodified

View fixture on GitHub

1		namespace Shop
2		{
3		public static class Text
4		{
5		public static string Shout(this string text) => text.ToUpperInvariant();
6
7		public static string Maybe(string text) => text?.Shout();
8		}
9		}

1	1		using System.Collections.Generic;
2	2
3	3		namespace Shop
4	4		{
5	5		public class Basket
6	6		{
7	7		private readonly List<int> _quantities = new List<int>();
8	8
9		−	public int First() => _quantities.FirstOr(0);
	9	+	public int First() => Sequences.FirstOr(_quantities, 0);
10	10
11		−	public string FirstName(List<string> names) => names.FirstOr<string>("none");
	11	+	public string FirstName(List<string> names) => Sequences.FirstOr<string>(names, "none");
12	12		}
13	13		}

1	1		using System.Collections.Generic;
2	2
3	3		namespace Shop
4	4		{
5	5		public static class Sequences
6	6		{
7		−	public static T FirstOr<T>(this IEnumerable<T> items, T fallback)
	7	+	public static T FirstOr<T>(IEnumerable<T> items, T fallback)
8	8		{
9	9		foreach (var item in items)
10	10		return item;
11	11		return fallback;
12	12		}
13	13		}
14	14		}

1	1		namespace Shop.Text
2	2		{
3	3		public static class Formatting
4	4		{
5		−	public static string Trimmed(this string text) => text.Trim();
	5	+	public static string Trimmed(string text) => text.Trim();
6	6		}
7	7		}

1	1		using Shop.Text;
2	2
3	3		namespace Reports
4	4		{
5	5		public class Report
6	6		{
7		−	public string Title(string raw) => raw.Trimmed().ToUpperInvariant();
	7	+	public string Title(string raw) => Formatting.Trimmed(raw).ToUpperInvariant();
8	8
9		−	public int Length(string raw) => (raw + " ").Trimmed().Length;
	9	+	public int Length(string raw) => Formatting.Trimmed(raw + " ").Length;
10	10		}
11	11		}

1		namespace Shop
2		{
3		public static class Text
4		{
5		public static string Shout(string text) => text.ToUpperInvariant();
6		}
7		}

1	1		namespace Shop
2	2		{
3	3		public class Checkout
4	4		{
5		−	public string Welcome(string name) => name.Shout();
	5	+	public string Welcome(string name) => Text.Shout(name);
6	6
7	7		public string Static(string name) => Text.Shout(name);
8	8		}
9	9		}

1	1		namespace Shop
2	2		{
3	3		public static class Text
4	4		{
5	5		// Used for headings.
6		−	public static string Shout(this string text) => text.ToUpperInvariant() + "!";
	6	+	public static string Shout(string text) => text.ToUpperInvariant() + "!";
7	7
8		−	public static string Greet(string name) => ("hello " + name).Shout();
	8	+	public static string Greet(string name) => Shout("hello " + name);
9	9		}
10	10		}