Catalog / Primitives / convert-to-expression-body

Convert to Expression Body

Replaces a block body holding a single statement with an expression body. The reverse of Convert to Block Body.

Target

The declaration, by symbol: a method, constructor, operator, property, indexer or accessor (M:Sample.set_Name(System.String) for a setter). A local function, which has no symbol id, by a caret on its name.

Precondition

The declaration has a block body, not an expression body and not none, as an abstract member or an auto-property has.
The block holds exactly one statement: return expression;, an expression statement, or throw expression;.
The block contains no preprocessor directive.
A property or indexer has a get accessor and nothing else, with no modifiers or attributes on it. A property with a setter as well is converted one accessor at a time.

Transformation

{ return expression; } and { expression; } become => expression;.
{ throw expression; } becomes => throw expression;.
A property or indexer whose only accessor is a get accessor becomes an expression-bodied property or indexer: public string Name => _name;.
The expression follows the header on the same line. An expression spanning several lines keeps its line breaks, shifted to follow the header.
A constructor initializer and a generic constraint clause stay before the arrow.

Preserved

Behaviour: an expression body means exactly what the single statement did.
Comments inside the block move to lines of their own above the declaration, below any documentation comment; a comment after the statement stays at the end of the line.

Limitations

A comment between return and its expression, or after the header before the block, is not kept.
Accessors with attributes or modifiers of their own keep their property's accessor list; only the accessor itself can be converted.

Error codes

Code	Meaning
`not-single-statement`	the body is not a single return, expression or throw statement
`several-accessors`	the property has more than a plain get accessor
`already-expression-bodied`	the declaration already has an expression body
`directive-in-body`	the body contains a preprocessor directive
`no-body`	the declaration has no body, such as an abstract method
`not-a-member-with-body`	the target is not a method, property, accessor, constructor, operator or local function

Cases

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

#accessor

One accessor of a property with a getter and a setter becomes expression-bodied

success

Targetsymbol M:Sample.set_Name(System.String)

Sample.csmodified

1	1		public class Sample
2	2		{
3	3		private string _name = "";
4	4
5	5		public string Name
6	6		{
7	7		get { return _name; }
8		−	set
9		−	{
10		−	_name = value.Trim();
11		−	}
	8	+	set => _name = value.Trim();
12	9		}
13	10		}

1		public class Sample
2		{
3		private int _a;
4
5		public int Total() => _a;
6		}

1	1		namespace Shop;
2	2
3	3		public class Entity
4	4		{
5	5		}
6	6
7	7		public class Order : Entity
8	8		{
9	9		private readonly int _quantity;
10	10
11		−	public Order(int quantity) : base()
12		−	{
13		−	_quantity = quantity;
14		−	}
	11	+	public Order(int quantity) : base() => _quantity = quantity;
15	12		}

1		using System;
2
3		public class Sample
4		{
5		public void Log(string message)
6		{
7		#if DEBUG
8		Console.WriteLine("debug: " + message);
9		#else
10		Console.WriteLine(message);
11		#endif
12		}
13		}

1	1		using System;
2	2
3	3		public class Sample
4	4		{
5		−	public T Larger<T>(T a, T b) where T : IComparable<T>
6		−	{
7		−	return a.CompareTo(b) >= 0 ? a : b;
8		−	}
	5	+	public T Larger<T>(T a, T b) where T : IComparable<T> => a.CompareTo(b) >= 0 ? a : b;
9	6		}

1	1		public class Sample
2	2		{
3	3		private int _a;
4	4		private int _b;
5	5
6	6		/// <summary>The sum of both parts.</summary>
7		−	public int Total()
8		−	{
9		−	// Overflow is not expected here.
10		−	return _a + _b; // unchecked
11		−	}
	7	+	// Overflow is not expected here.
	8	+	public int Total() => _a + _b; // unchecked
12	9
13	10		public int Difference() => _a - _b;
14	11		}

1	1		public class Sample
2	2		{
3	3		public int Total(int[] prices)
4	4		{
5	5		var sum = 0;
6	6		foreach (var price in prices)
7	7		sum += WithTax(price);
8	8		return sum;
9	9
10		−	static int /^/WithTax(int price)
11		−	{
12		−	return price * 120 / 100;
13		−	}
	10	+	static int WithTax(int price) => price * 120 / 100;
14	11		}
15	12		}

1	1		using System.Collections.Generic;
2	2		using System.Linq;
3	3
4	4		public class Sample
5	5		{
6		−	public int Total(List<int> items)
7		−	{
8		−	return items
9		−	.Where(i => i > 0)
10		−	.Sum();
11		−	}
	6	+	public int Total(List<int> items) => items
	7	+	.Where(i => i > 0)
	8	+	.Sum();
12	9		}

1		public abstract class Shape
2		{
3		public abstract double Area();
4		}

1		public class Sample
2		{
3		private int _total;
4
5		public int Total => _total;
6		}

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

1	1		namespace Shop;
2	2
3	3		public readonly struct Money
4	4		{
5	5		public Money(decimal amount)
6	6		{
7	7		Amount = amount;
8	8		}
9	9
10	10		public decimal Amount { get; }
11	11
12		−	public static Money operator +(Money left, Money right)
13		−	{
14		−	return new Money(left.Amount + right.Amount);
15		−	}
	12	+	public static Money operator +(Money left, Money right) => new Money(left.Amount + right.Amount);
16	13		}

1	1		public class Sample
2	2		{
3	3		public string Format(string text)
4	4		{
5	5		return text.Trim();
6	6		}
7	7
8		−	public string Format(int number)
9		−	{
10		−	return number.ToString();
11		−	}
	8	+	public string Format(int number) => number.ToString();
12	9		}

1	1		public class Sample
2	2		{
3	3		private string _first = "";
4	4		private string _last = "";
5	5
6		−	public string Name
7		−	{
8		−	get
9		−	{
10		−	return _first + " " + _last;
11		−	}
12		−	}
	6	+	public string Name => _first + " " + _last;
13	7		}

1	1		using System;
2	2
3	3		public class Sample
4	4		{
5		−	public int Next()
6		−	{
7		−	throw new NotSupportedException();
8		−	}
	5	+	public int Next() => throw new NotSupportedException();
9	6		}

Convert to Expression Body

Target

Precondition

Transformation

Preserved

Limitations

Error codes

Cases

#accessor

#already-expression-bodied-rejected

#constructor

#directive-in-body-rejected

#generic-method

#keeps-comments

#local-function

#multi-line-expression

#no-body-rejected

#not-a-member-rejected

#nullable-context

#operator

#overload

#read-only-property

#return-statement

#several-accessors-rejected

#several-statements-rejected

#throw-statement

#void-method