lib/collections.bzl

# Copyright 2017 The Bazel Authors. All rights reserved.
#
# 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.

"""Skylib module containing functions that operate on collections."""

def _after_each(separator, iterable):
    """Inserts `separator` after each item in `iterable`.

    Args:
      separator: The value to insert after each item in `iterable`.
      iterable: The list into which to intersperse the separator.

    Returns:
      A new list with `separator` after each item in `iterable`.
    """
    result = []
    for x in iterable:
        result.append(x)
        result.append(separator)

    return result

def _before_each(separator, iterable):
    """Inserts `separator` before each item in `iterable`.

    Args:
      separator: The value to insert before each item in `iterable`.
      iterable: The list into which to intersperse the separator.

    Returns:
      A new list with `separator` before each item in `iterable`.
    """
    result = []
    for x in iterable:
        result.append(separator)
        result.append(x)

    return result

def _uniq(iterable):
    """Returns a list of unique elements in `iterable`.

    Requires all the elements to be hashable.

    Args:
      iterable: An iterable to filter.

    Returns:
      A new list with all unique elements from `iterable`.
    """
    unique_elements = {element: None for element in iterable}

    # list() used here for python3 compatibility.
    # TODO(bazel-team): Remove when testing frameworks no longer require python compatibility.
    return list(unique_elements.keys())

collections = struct(
    after_each = _after_each,
    before_each = _before_each,
    uniq = _uniq,
)