Add StringJoinSubstitution substituion

launch/launch/substitutions/__init__.py

@@ -34,6 +34,7 @@
 from .not_equals_substitution import NotEqualsSubstitution
 from .path_join_substitution import PathJoinSubstitution
 from .python_expression import PythonExpression
+from .string_join_substitution import StringJoinSubstitution
 from .substitution_failure import SubstitutionFailure
 from .text_substitution import TextSubstitution
 from .this_launch_file import ThisLaunchFile
@@ -60,6 +61,7 @@
     'OrSubstitution',
     'PathJoinSubstitution',
     'PythonExpression',
+    'StringJoinSubstitution',
     'SubstitutionFailure',
     'TextSubstitution',
     'ThisLaunchFile',

launch/launch/substitutions/string_join_substitution.py

@@ -0,0 +1,98 @@
+# Copyright 2025 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Module for the StringJoinSubstitution substitution."""
+
+from typing import Iterable, List, Text
+
+from ..launch_context import LaunchContext
+from ..some_substitutions_type import SomeSubstitutionsType
+from ..substitution import Substitution
+from ..utilities import perform_substitutions
+
+
+class StringJoinSubstitution(Substitution):
+    """
+    Substitution that joins strings and/or other substitutions.
+
+    This takes in a list of string components as substitutions.
+    The substitutions for each string component are performed and concatenated,
+    and then all string components are joined with a specified delimiter as seperation.
+
+    For example:
+
+    .. code-block:: python
+
+        StringJoinSubstitution(
+            [['https', '://'], LaunchConfiguration('subdomain')], 'ros', 'org'],
+            delimiter='.'
+        )
+
+    If the ``subdomain`` launch configuration was set to ``docs``
+    and the ``delimiter`` to ``.``, this would result in a string equal to
+
+    .. code-block:: python
+
+        'https://docs.ros.org'
+    """
+
+    def __init__(
+        self,
+        substitutions: Iterable[SomeSubstitutionsType],
+        delimiter: SomeSubstitutionsType = '',
+    ) -> None:
+        """
+        Create a StringJoinSubstitution.
+
+        :param substitutions: the list of string component substitutions to join
+        :param delimiter: the text inbetween two consecutive components (default no text)
+        """
+        from ..utilities import normalize_to_list_of_substitutions
+
+        self.__substitutions = [
+            normalize_to_list_of_substitutions(string_component_substitutions)
+            for string_component_substitutions in substitutions
+        ]
+        self.__delimiter = normalize_to_list_of_substitutions(delimiter)
+
+    @property
+    def substitutions(self) -> List[List[Substitution]]:
+        """Getter for substitutions."""
+        return self.__substitutions
+
+    @property
+    def delimiter(self) -> List[Substitution]:
+        """Getter for delimiter."""
+        return self.__delimiter
+
+    def __repr__(self) -> Text:
+        """Return a description of this substitution as a string."""
+        string_components = [
+            ' + '.join([s.describe() for s in component_substitutions])
+            for component_substitutions in self.substitutions
+        ]
+        delimiter_component = ' + '.join([d.describe() for d in self.delimiter])
+        return (
+            f'StringJoinSubstitution(['
+            f'{", ".join(string_components)}], delimiter={delimiter_component})'
+        )
+
+    def perform(self, context: LaunchContext) -> Text:
+        """Perform the substitution by retrieving the local variable."""
+        string_components = [
+            perform_substitutions(context, component_substitutions)
+            for component_substitutions in self.substitutions
+        ]
+        delimiter_component = perform_substitutions(context, self.delimiter)
+        return delimiter_component.join(string_components)

launch/test/launch/substitutions/test_string_join_substitution.py

@@ -0,0 +1,71 @@
+# Copyright 2025 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tests for the StringJoinSubstitution substitution class."""
+
+from launch import LaunchContext
+from launch.substitutions import StringJoinSubstitution
+from launch.substitutions import TextSubstitution
+
+
+def test_string_join():
+    context = LaunchContext()
+
+    strings = ['abc', 'def', 'ghi']
+    sub = StringJoinSubstitution(strings)
+    assert sub.perform(context) == ''.join(strings)
+
+    strings = ['abc', ['def'], [TextSubstitution(text='ghi'), 'jkl'], TextSubstitution(text='mno')]
+    sub_with_sub = StringJoinSubstitution(strings)
+    assert sub_with_sub.perform(context) == 'abcdefghijklmno'
+
+
+def test_string_join_with_delimiter():
+    context = LaunchContext()
+
+    strings = ['abc', 'def', 'ghi']
+    sub = StringJoinSubstitution(strings, delimiter='.')
+    assert sub.perform(context) == '.'.join(strings)
+
+    strings = ['abc', ['def'], [TextSubstitution(text='ghi'), 'jkl'], TextSubstitution(text='mno')]
+    sub_with_sub = StringJoinSubstitution(strings, delimiter='.')
+    assert sub_with_sub.perform(context) == 'abc.def.ghijkl.mno'
+
+
+def test_string_join_with_substitution_delimiter():
+    context = LaunchContext()
+
+    strings = ['abc', 'def', 'ghi']
+    sub = StringJoinSubstitution(strings, delimiter=['-', '.', '-'])
+    assert sub.perform(context) == '-.-'.join(strings)
+
+    strings = ['abc', ['def'], [TextSubstitution(text='ghi'), 'jkl'], TextSubstitution(text='mno')]
+    sub_with_sub = StringJoinSubstitution(strings, delimiter=['-', '.', '-'])
+    assert sub_with_sub.perform(context) == 'abc-.-def-.-ghijkl-.-mno'
+
+    strings = ['abc', 'def', 'ghi']
+    sub = StringJoinSubstitution(strings, delimiter=TextSubstitution(text='_'))
+    assert sub.perform(context) == '_'.join(strings)
+
+    strings = ['abc', ['def'], [TextSubstitution(text='ghi'), 'jkl'], TextSubstitution(text='mno')]
+    sub_with_sub = StringJoinSubstitution(strings, delimiter=TextSubstitution(text='_'))
+    assert sub_with_sub.perform(context) == 'abc_def_ghijkl_mno'
+
+    strings = ['abc', 'def', 'ghi']
+    sub = StringJoinSubstitution(strings, delimiter=['(^', TextSubstitution(text='_'), '^)'])
+    assert sub.perform(context) == '(^_^)'.join(strings)
+
+    strings = ['abc', ['def'], [TextSubstitution(text='ghi'), 'jkl'], TextSubstitution(text='mno')]
+    sub_with_sub = StringJoinSubstitution(strings, delimiter=[TextSubstitution(text='(^_'), '^)'])
+    assert sub_with_sub.perform(context) == 'abc(^_^)def(^_^)ghijkl(^_^)mno'