gen_switch.py

#!/usr/bin/env python3

# Copyright 2021 gRPC authors.
#
# 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.

import sys


# utility: print a big comment block into a set of files
def put_banner(files, banner):
    for f in files:
        print("/*", file=f)
        for line in banner:
            print(" * %s" % line, file=f)
        print(" */", file=f)
        print("", file=f)


with open("src/core/lib/promise/detail/switch.h", "w") as H:
    # copy-paste copyright notice from this file
    with open(sys.argv[0]) as my_source:
        copyright = []
        for line in my_source:
            if line[0] != "#":
                break
        for line in my_source:
            if line[0] == "#":
                copyright.append(line)
                break
        for line in my_source:
            if line[0] != "#":
                break
            copyright.append(line)
        put_banner([H], [line[2:].rstrip() for line in copyright])

    put_banner([H], ["Automatically generated by %s" % sys.argv[0]])

    print("#ifndef GRPC_CORE_LIB_PROMISE_DETAIL_SWITCH_H", file=H)
    print("#define GRPC_CORE_LIB_PROMISE_DETAIL_SWITCH_H", file=H)
    print("", file=H)
    print("#include <grpc/support/port_platform.h>", file=H)
    print("", file=H)
    print("#include <stdlib.h>", file=H)
    print("", file=H)
    print("namespace grpc_core {", file=H)

    for n in range(1, 33):
        print("", file=H)
        print(
            "template <typename R, %s> R Switch(char idx, %s) {"
            % (
                ", ".join("typename F%d" % i for i in range(0, n)),
                ", ".join("F%d f%d" % (i, i) for i in range(0, n)),
            ),
            file=H,
        )
        print("  switch (idx) {", file=H)
        for i in range(0, n):
            print("   case %d: return f%d();" % (i, i), file=H)
        print("  }", file=H)
        print("  abort();", file=H)
        print("}", file=H)

    print("", file=H)
    print("}", file=H)
    print("", file=H)
    print("#endif // GRPC_CORE_LIB_PROMISE_DETAIL_SWITCH_H", file=H)