StringBuilder

StringBuilder

Suggests replacing expressions with equivalent expressions that are more readable or improving performance. The analyzer doesn't make any suggestions if the current language version doesn't support the replacement or the target framework doesn't contain the target method (or method overload).

In the following examples the text represents any string expression.

Append

• StringBuilder Append(char value, int repeatCount)
• StringBuilder Append(char[]? value)
• StringBuilder Append(char[]? value, int startIndex, int charCount)
• StringBuilder Append(string? value)
• StringBuilder Append(string? value, int startIndex, int count)
• StringBuilder Append(StringBuilder? value)
• StringBuilder Append(StringBuilder? value, int startIndex, int count)
• StringBuilder Append(object? value)

Case	Suggested replacement	When suggested
builder.Append(null)	builder	value is null
builder.Append(c, 0)	builder	repeatCount is a 0
builder.Append(c, 1)	builder.Append(c)	repeatCount is a 1
builder.Append([])	builder	value is an empty array
builder.Append(null, 0, 0)	builder	value is null, startIndex and charCount are both 0
builder.Append([], 0, 0)	builder	value is an empty array, startIndex and charCount are both 0
builder.Append("")	builder	value is an empty string
builder.Append("a")	builder.Append('a')	value is a one-character constant string
builder.Append(null, 0, 0)	builder	value is null, startIndex and count are both 0
builder.Append(s, startIndex, 0)	builder	s is not null here, startIndex is a non-negative constant value, and count is 0
builder.Append(sb, startIndex, 0)	builder	sb is not null here, startIndex is a non-negative constant value, and count is 0
builder.Append("abc", 1, 1)	builder.Append('b')	s is a constant string, startIndex is constants indicating a valid position within s, and count is 1

where c is a char value, s is a string, sb is a StringBuilder, and startIndex and count are int values.

AppendJoin

• StringBuilder AppendJoin(string? separator, params object?[] values)
• StringBuilder AppendJoin(string? separator, params ReadOnlySpan<object?> values)
• StringBuilder AppendJoin<T>(string? separator, IEnumerable<T> values)
• StringBuilder AppendJoin(string? separator, params string?[] values)
• StringBuilder AppendJoin(string? separator, params ReadOnlySpan<string?> values)
• StringBuilder AppendJoin(char separator, params object?[] values)
• StringBuilder AppendJoin(char separator, params ReadOnlySpan<object?> values)
• StringBuilder AppendJoin<T>(char separator, IEnumerable<T> values)
• StringBuilder AppendJoin(char separator, params string?[] values)
• StringBuilder AppendJoin(char separator, params ReadOnlySpan<string?> values)

Case	Suggested replacement	When suggested
builder.AppendJoin(separator, [])	builder	values is an empty array, collection, or span expression
builder.AppendJoin(separator, [item])	builder.Append(item)	values consists of a single item
builder.AppendJoin(",", values)	builder.AppendJoin(',', values)	separator a one-character constant string

where separator is a string or a char value, values is an array, an IEnumerable<T>, ReadOnlySpan<object?>, or ReadOnlySpan<string?>.

Insert

• StringBuilder Insert(int index, string? value, int count)
• StringBuilder Insert(int index, string? value)
• StringBuilder Insert(int index, object? value)

Case	Suggested replacement	When suggested
builder.Insert(index, s, 1)	builder.Insert(index, s)	count is 1
builder.Insert(index, "a", 1)	builder.Insert(index, 'a')	value is a one-character constant string and count is 1
builder.Insert(index, "a")	builder.Insert(index, 'a')	value is a one-character constant string
builder.Insert(index, null)	builder	value is null

where index is an int value, s is a string, and count is an int value.

Replace

• StringBuilder Replace(char oldChar, char newChar)
• StringBuilder Replace(string oldValue, string? newValue)
• StringBuilder Replace(string oldValue, string? newValue, int startIndex, int count)

Case	Suggested replacement	When suggested
builder.Replace('a', 'b')	builder.Replace('a', 'b')	oldValue and newValue are one-character constant strings
builder.Replace("abc", "abc")	builder	oldValue is a constant non-empty string and newValue is a constant string indentical to oldValue
builder.Replace("a", "b")	builder.Replace('a', 'b')	oldValue and newValue are one-character constant strings
builder.Replace("a", "b", startIndex, count)	builder.Replace('a', 'b', , startIndex, count)	oldValue and newValue are one-character constant strings

where startIndex and count are int values.

💡 Quick-fixes are available.

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References

• CA1834: Use StringBuilder.Append(char) for single character strings