Regular Expressions Assistance

ReSharper provides a rich set of tools to work with .NET regular expressions. You can quickly analyze existing expressions, find and fix errors. When typing new expressions, ReSharper helps with automatic completion and validation.

In this topic:

Regular expressions and strings
Highlighting
Fixing errors
Validating and testing
IntelliSense
Extracting precompiled regular expression

Regular expressions and strings

By default, ReSharper only processes regular expressions in the pattern parameter, in methods of the Regex class. However, strings containing regular expression can be defined in different places: string constants, fields, other methods' arguments, etc. If you want ReSharper to process these strings as regular expressions, you have two options. One way is to mark any string as a regular expression using a context action.

To process regular expressions outside of Regex class methods

Set the caret on a string containing regular expressions
Press Alt+Enter or click on the action indicator to the left of the caret to open the action list.
Choose the Make regular expression here context action.
If you decide later to disable processing the string as a regular expression, you can use the Remove regular expression context action.

Another way is to annotate parameters of your own methods as regular expressions using the [RegexPatternAttribute] from JetBrains.Annotations.

To process regular expressions in method arguments

Reference the JetBrains.Annotations namespace in your project. For more information, see Annotations in Source Code
Annotate a parameter that should receive a regular expression with the [RegexPatternAttribute].

ReSharper will process the corresponding arguments in method calls as regular expressions:

Highlighting

ReSharper highlights syntax constructs as well as errors and redundancies in regular expressions:

Highlighting colors have the following meanings:

Light Blue – character classes, anchors and quantifiers
Light Green – grouping constructs
Orange – set constructs
Pink and light pink – escape sequence
Green – comments
Red with curly underline – errors
Blue curly underline – warnings

Matching brackets in groups, group names and sets are highlighted when you set a caret to one of the delimiters. You can toggle and adjust this highlighting using the Highlight matching delimiters setting in ReSharper Options | Environment | Editor | Editor Appearance.

By default, ReSharper highlights correct and incorrect escape sequences in all non-verbatim strings:

If necessary, you can turn this highlighting of by clearing the Highlight special characters in string literals check box on the Code Inspection | Settings options page.

Fixing errors

To fix errors in regular expressions, set the caret at the red highlight, press Alt+Enter, and then select the corresponding quick-fix.

The most common example of a regular expression error is a misuse of the escape characters.

ReSharper helps you fix the error automatically:

Validating and testing

ReSharper allows you to validate and test your regular expression patterns at design time or while debugging. In the Validate Regular Expression dialog box, you can enter various sample strings and see how your regular expression matches these strings. The dialog box is available in the main menu: ReSharper | Tools | Validate Regular Expression. Using this dialog, you can fix your expression and make sure that you get the desired matching.

ReSharper applies the standard .NET regular expression engine for processing ao the expression works exactly the same way as it would in runtime. All matches in sample strings are highlighted.

Also, the matches are displayed in a tree view by matches, groups in matches and all captures for groups (if there are more than two of them). You can select nodes in the tree to highlight corresponding parts of the sample strings and groups in regular expression (if a group or capture is selected).

To validate a regular expression in your code

Set the caret at a regular expression.
Press Alt+Enter or click on the action indicator to the left of the caret to open the action list.
Choose the Validate regular expression context action.
In the Validate Regular Expression dialog box that opens, provide some sample strings in the Test Input area.
To test several sample strings simultaneously, separate the strings with a new line and check the Check lines separately check box. Note that in this case, the samples should be single-line strings.
If necessary, you can change engine the regular expression options in the Options drop down list.
If the regular expression works as expected, click Insert to insert it back in the code.

IntelliSense

ReSharper provides IntelliSense support for almost all .NET regular expression constructs. In the completion list, each construct is shown with a brief description.

In regular expressions, you can use four types of IntelliSense:

Automatic completion - triggered after the \, ( and [ characters
Basic completion (Ctrl+Space) – shows elements, available for the current scope
Smart completion (Ctrl+Shift+Space) – shows most probable elements for the current scope
Double completion ( Ctrl+Space twice) – shows all possible elements

You can also benefit from ReSharper's Intellisense when using the Match.Groups Property. ReSharper detects group names in the expression and suggests them in the completion list:

Extracting precompiled regular expression

If you need to reuse a regular expression, which is used in a static method of the Regex class, you can extract it to a precompiled regular expression.

To extract the regular expression, set the caret anywhere in the method call, press Alt+Enter and choose the To precompiled Regex context action.

For example, you can extract the regular expression from the pattern parameter of the IsMatch method:

public void Bar()
        {
            var result = Regex.IsMatch("Input", "Pattern");
        }

After applying the context action, the pattern is extracted into a static field:

private static readonly Regex Regex1 = new Regex("Pattern");

        public void Bar()
        {
            var result = Regex1.IsMatch("Input");
        }

This feature is supported in the following languages/technologies:

C#	VB.NET	C++	HTML	ASPX	Razor	JavaScript	TypeScript	CSS	XML	XAML	RESX	Build Scripts	Protobuf	JSON

Concepts:

Coding Assistance

External Links:

Last modified: 19 August 2016

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