# Source code for ufl.referencevalue

    """Representation of the reference value of a function."""
    # Copyright (C) 2008-2016 Martin Sandve Alnæs
    #
    # This file is part of UFL (https://www.fenicsproject.org)
    #
    # SPDX-License-Identifier:    LGPL-3.0-or-later

    from ufl.core.operator import Operator
    from ufl.core.terminal import FormArgument
    from ufl.core.ufl_type import ufl_type

    @ufl_type(num_ops=1, is_index_free=True, is_terminal_modifier=True, is_in_reference_frame=True)
    class ReferenceValue(Operator):
        """Representation of the reference cell value of a form argument."""

        __slots__ = ()

        def __init__(self, f):
            """Initialise."""
            if not isinstance(f, FormArgument):
                raise ValueError("Can only take reference value of form arguments.")
            Operator.__init__(self, (f,))

        @property
        def ufl_shape(self):
            """Get the UFL shape."""
            return self.ufl_operands[0].ufl_element().reference_value_shape

        def evaluate(self, x, mapping, component, index_values, derivatives=()):
            """Get child from mapping and return the component asked for."""
            raise NotImplementedError()

        def __str__(self):
            """Format as a string."""
            return f"reference_value({self.ufl_operands[0]})"