API reference - Class Expression

Notation used in Ruby API documentation

Module: tl

Description: Evaluation of Expressions

Class hierarchy: Expression » ExpressionContext

This class allows evaluation of expressions. Expressions are used in many places throughout KLayout and provide computation features for various applications. Having a script language, there is no real use for expressions inside a script client. This class is provided mainly for testing purposes.

An expression is 'compiled' into an Expression object and can be evaluated multiple times.

This class has been introduced in version 0.25. In version 0.26 it was separated into execution and context.

Public constructors

new Expression ptrnew(string expr)Creates an expression evaluator
new Expression ptrnew(string expr,
map<string,variant> variables)
Creates an expression evaluator

Public methods

void_createEnsures the C++ object is created
void_destroyExplicitly destroys the object
[const]bool_destroyed?Returns a value indicating whether the object was already destroyed
[const]bool_is_const_object?Returns a value indicating whether the reference is a const reference
void_manageMarks the object as managed by the script side.
void_unmanageMarks the object as no longer owned by the script side.
variantevalEvaluates the current expression and returns the result
voidtext=(string expr)Sets the given text as the expression.

Public static methods and constants

varianteval(string expr)A convience function to evaluate the given expression and directly return the result

Detailed description

_create

Signature: void _create

Description: Ensures the C++ object is created

Use this method to ensure the C++ object is created, for example to ensure that resources are allocated. Usually C++ objects are created on demand and not necessarily when the script object is created.

_destroy

Signature: void _destroy

Description: Explicitly destroys the object

Explicitly destroys the object on C++ side if it was owned by the script interpreter. Subsequent access to this object will throw an exception. If the object is not owned by the script, this method will do nothing.

_destroyed?

Signature: [const] bool _destroyed?

Description: Returns a value indicating whether the object was already destroyed

This method returns true, if the object was destroyed, either explicitly or by the C++ side. The latter may happen, if the object is owned by a C++ object which got destroyed itself.

_is_const_object?

Signature: [const] bool _is_const_object?

Description: Returns a value indicating whether the reference is a const reference

This method returns true, if self is a const reference. In that case, only const methods may be called on self.

_manage

Signature: void _manage

Description: Marks the object as managed by the script side.

After calling this method on an object, the script side will be responsible for the management of the object. This method may be called if an object is returned from a C++ function and the object is known not to be owned by any C++ instance. If necessary, the script side may delete the object if the script's reference is no longer required.

Usually it's not required to call this method. It has been introduced in version 0.24.

_unmanage

Signature: void _unmanage

Description: Marks the object as no longer owned by the script side.

Calling this method will make this object no longer owned by the script's memory management. Instead, the object must be managed in some other way. Usually this method may be called if it is known that some C++ object holds and manages this object. Technically speaking, this method will turn the script's reference into a weak reference. After the script engine decides to delete the reference, the object itself will still exist. If the object is not managed otherwise, memory leaks will occur.

Usually it's not required to call this method. It has been introduced in version 0.24.

eval

(1) Signature: variant eval

Description: Evaluates the current expression and returns the result

Python specific notes:
This instance method is available as '_inst_eval' in Python.

(2) Signature: [static] variant eval (string expr)

Description: A convience function to evaluate the given expression and directly return the result

This is a static method that does not require instantiation of the expression object first.

Python specific notes:
This class method is available as '_class_eval' in Python.

new

(1) Signature: [static] new Expression ptr new (string expr)

Description: Creates an expression evaluator

Python specific notes:
This method is the default initializer of the object.

(2) Signature: [static] new Expression ptr new (string expr, map<string,variant> variables)

Description: Creates an expression evaluator

This version of the constructor takes a hash of variables available to the expressions.

Python specific notes:
This method is the default initializer of the object.

text=

Signature: void text= (string expr)

Description: Sets the given text as the expression.

Python specific notes:
The object exposes a writable attribute 'text'. This is the setter.