godot-docs/classes/class_expression.rst

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.. _class_Expression:

Expression
==========

**Inherits:** :ref:`RefCounted<class_RefCounted>` **<** :ref:`Object<class_Object>`

A class that stores an expression you can execute.

.. rst-class:: classref-introduction-group

Description
-----------

An expression can be made of any arithmetic operation, built-in math function call, method call of a passed instance, or built-in type construction call.

An example expression text using the built-in math functions could be ``sqrt(pow(3, 2) + pow(4, 2))``.

In the following example we use a :ref:`LineEdit<class_LineEdit>` node to write our expression and show the result.


.. tabs::

 .. code-tab:: gdscript

    var expression = Expression.new()
    
    func _ready():
        $LineEdit.text_submitted.connect(self._on_text_submitted)
    
    func _on_text_submitted(command):
        var error = expression.parse(command)
        if error != OK:
            print(expression.get_error_text())
            return
        var result = expression.execute()
        if not expression.has_execute_failed():
            $LineEdit.text = str(result)

 .. code-tab:: csharp

    private Expression _expression = new Expression();
    
    public override void _Ready()
    {
        GetNode<LineEdit>("LineEdit").TextSubmitted += OnTextEntered;
    }
    
    private void OnTextEntered(string command)
    {
        Error error = _expression.Parse(command);
        if (error != Error.Ok)
        {
            GD.Print(_expression.GetErrorText());
            return;
        }
        Variant result = _expression.Execute();
        if (!_expression.HasExecuteFailed())
        {
            GetNode<LineEdit>("LineEdit").Text = result.ToString();
        }
    }



.. rst-class:: classref-introduction-group

Tutorials
---------

- :doc:`Evaluating Expressions <../tutorials/scripting/evaluating_expressions>`

.. rst-class:: classref-reftable-group

Methods
-------

.. table::
   :widths: auto

   +---------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | :ref:`Variant<class_Variant>`         | :ref:`execute<class_Expression_method_execute>`\ (\ inputs\: :ref:`Array<class_Array>` = [], base_instance\: :ref:`Object<class_Object>` = null, show_error\: :ref:`bool<class_bool>` = true, const_calls_only\: :ref:`bool<class_bool>` = false\ ) |
   +---------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | :ref:`String<class_String>`           | :ref:`get_error_text<class_Expression_method_get_error_text>`\ (\ ) |const|                                                                                                                                                                         |
   +---------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | :ref:`bool<class_bool>`               | :ref:`has_execute_failed<class_Expression_method_has_execute_failed>`\ (\ ) |const|                                                                                                                                                                 |
   +---------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | :ref:`Error<enum_@GlobalScope_Error>` | :ref:`parse<class_Expression_method_parse>`\ (\ expression\: :ref:`String<class_String>`, input_names\: :ref:`PackedStringArray<class_PackedStringArray>` = PackedStringArray()\ )                                                                  |
   +---------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

.. rst-class:: classref-section-separator

----

.. rst-class:: classref-descriptions-group

Method Descriptions
-------------------

.. _class_Expression_method_execute:

.. rst-class:: classref-method

:ref:`Variant<class_Variant>` **execute**\ (\ inputs\: :ref:`Array<class_Array>` = [], base_instance\: :ref:`Object<class_Object>` = null, show_error\: :ref:`bool<class_bool>` = true, const_calls_only\: :ref:`bool<class_bool>` = false\ ) :ref:`🔗<class_Expression_method_execute>`

Executes the expression that was previously parsed by :ref:`parse<class_Expression_method_parse>` and returns the result. Before you use the returned object, you should check if the method failed by calling :ref:`has_execute_failed<class_Expression_method_has_execute_failed>`.

If you defined input variables in :ref:`parse<class_Expression_method_parse>`, you can specify their values in the inputs array, in the same order.

.. rst-class:: classref-item-separator

----

.. _class_Expression_method_get_error_text:

.. rst-class:: classref-method

:ref:`String<class_String>` **get_error_text**\ (\ ) |const| :ref:`🔗<class_Expression_method_get_error_text>`

Returns the error text if :ref:`parse<class_Expression_method_parse>` or :ref:`execute<class_Expression_method_execute>` has failed.

.. rst-class:: classref-item-separator

----

.. _class_Expression_method_has_execute_failed:

.. rst-class:: classref-method

:ref:`bool<class_bool>` **has_execute_failed**\ (\ ) |const| :ref:`🔗<class_Expression_method_has_execute_failed>`

Returns ``true`` if :ref:`execute<class_Expression_method_execute>` has failed.

.. rst-class:: classref-item-separator

----

.. _class_Expression_method_parse:

.. rst-class:: classref-method

:ref:`Error<enum_@GlobalScope_Error>` **parse**\ (\ expression\: :ref:`String<class_String>`, input_names\: :ref:`PackedStringArray<class_PackedStringArray>` = PackedStringArray()\ ) :ref:`🔗<class_Expression_method_parse>`

Parses the expression and returns an :ref:`Error<enum_@GlobalScope_Error>` code.

You can optionally specify names of variables that may appear in the expression with ``input_names``, so that you can bind them when it gets executed.

.. |virtual| replace:: :abbr:`virtual (This method should typically be overridden by the user to have any effect.)`
.. |const| replace:: :abbr:`const (This method has no side effects. It doesn't modify any of the instance's member variables.)`
.. |vararg| replace:: :abbr:`vararg (This method accepts any number of arguments after the ones described here.)`
.. |constructor| replace:: :abbr:`constructor (This method is used to construct a type.)`
.. |static| replace:: :abbr:`static (This method doesn't need an instance to be called, so it can be called directly using the class name.)`
.. |operator| replace:: :abbr:`operator (This method describes a valid operator to use with this type as left-hand operand.)`
.. |bitfield| replace:: :abbr:`BitField (This value is an integer composed as a bitmask of the following flags.)`
.. |void| replace:: :abbr:`void (No return value.)`