Rider Help

Evaluating Expressions

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Rider enables you to evaluate expressions and code fragments in the context of a stack frame currently selected in the Frames pane of the Debug tool window.

In addition to regular expressions, you can also evaluate operator expressions, lambda expressions, and anonymous classes.

The following evaluation modes are available:


While using the Expression Evaluation feature, be aware of the following:

  • A method can be invoked within the Expression Evaluation dialog only if the debugger has stopped at a breakpoint, but has not been paused.
  • Expression Evaluation can only be "single-level". In other words, if Rider stops at a breakpoint within a method called from the Expression Evaluation, you cannot use the Expression Evaluation feature again.

Evaluating arbitrary expressions

  1. Open the Evaluate Expression dialog box in one of the following ways:
    • Choose Run | Evaluate Expression on the main menu.
    • PressAlt+F8.
    • To evaluate a specific variable, select it on the Variables pane of the Debug tool window, then choose Run | Evaluate Expression or press Alt+F8.
  2. In the Evaluate Expression dialog box, specify the expression you want to evaluate. Do one of the following:
    • In the Expression field, type the expression in question or choose one of the previously evaluated expressions from the drop-down list.

      If you have selected a specific variable on the Variables pane, this variable will be displayed in the Expression text box.

    • To evaluate a code fragment, click the Code Fragment Mode button and fill in the Code Fragment text box.

      To return to the original mode, click the Expression mode button.

  3. Click the Evaluate button. The Result read-only field shows the evaluation output. If the specified expression cannot be evaluated, the Result field explains the reason.

Evaluating expressions in the editor

During a debugger session, the value of any expression is shown in the tooltip every time you hover your mouse pointer over it. If an expression contains children, clicking /help/img/idea/2017.2/add.png expands the node and displays all children.

You can also use the Quick Evaluate expression functionality that lets you view the value of an expression using the keyboard only.

There are two ways to evaluate an expression quickly:

  1. By using the Show value tooltip on code selection functionality:
    • In the Debugger | Data Views settings page, enable the Show value tooltip on code selection option.
    • Select a code fragment with the mouse, or by pressing Ctrl+Alt+Right. A tooltip with the expression value automatically appears under the selection and changes each time you change the selection.
  2. By manually invoking the tooltip with the expression value:
    • Place the caret at the desired location, or select an expression to be evaluated.
    • Choose Run | Quick Evaluate Expression on the main menu, or press Shift+F9. The tooltip with the expression value appears under the selected expression.
Last modified: 11 October 2017

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