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Commit b646b825 authored by Lloyd Pique's avatar Lloyd Pique
Browse files

Introduce ftl::ignore 

`ftl::ignore` works like `std::ignore`, but one can also ignore multiple
values using `operator()`. `ftl::ignore(a, b);` is more compact than
`std::ignore = a; std::ignore = b;`, and conveys the same idea.

Bug: 185536303
Flag: EXEMPT New library code
Test: atest ftl_test

Change-Id: Ice549328eeffb90f59f7b902809def48f583d157
parent ee449711

include/ftl/ignore.h

0 → 100644
+42 −0
Original line number Original line Diff line number Diff line 
/*

 * Copyright 2025 The Android Open Source Project

 *

 * 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.

 */



#pragma once



namespace android::ftl {



// An alternative to `std::ignore` that makes it easy to ignore multiple values.

//

// Examples:

//

//   void ftl_ignore_multiple(int arg1, const char* arg2, std::string arg3) {

//     // When invoked, all the arguments are ignored.

//     ftl::ignore(arg1, arg2, arg3);

//   }

//

//   void ftl_ignore_single(int arg) {

//     // It can be used like std::ignore to ignore a single value

//     ftl::ignore = arg;

//   }

//

inline constexpr struct {

  // NOLINTNEXTLINE(misc-unconventional-assign-operator, readability-named-parameter)

  constexpr auto operator=(auto&&) const -> decltype(*this) { return *this; }

  // NOLINTNEXTLINE(readability-named-parameter)

  constexpr void operator()(auto&&...) const {}

} ignore;



}  // namespace android::ftl
 
 No newline at end of file

libs/ftl/Android.bp

+1 −0
Original line number Original line Diff line number Diff line
@@ -26,6 +26,7 @@ cc_test { 
        "function_test.cpp",

        "function_test.cpp",

        "future_test.cpp",

        "future_test.cpp",

        "hash_test.cpp",

        "hash_test.cpp",

        "ignore_test.cpp",

        "match_test.cpp",

        "match_test.cpp",

        "mixins_test.cpp",

        "mixins_test.cpp",

        "non_null_test.cpp",

        "non_null_test.cpp",

libs/ftl/ignore_test.cpp

0 → 100644
+47 −0
Original line number Original line Diff line number Diff line 
/*

 * Copyright 2025 The Android Open Source Project

 *

 * 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.

 */



#include <string>



#include <ftl/ignore.h>

#include <gtest/gtest.h>



namespace android::test {

namespace {



// Keep in sync with the example usage in the header file.



void ftl_ignore_multiple(int arg1, const char* arg2, std::string arg3) {

  // When invoked, all the arguments are ignored.

  ftl::ignore(arg1, arg2, arg3);

}



void ftl_ignore_single(int arg) {

  // It can be used like std::ignore to ignore a single value

  ftl::ignore = arg;

}



}  // namespace



TEST(Ignore, Example) {

  // The real example test is that there are no compiler warnings for unused arguments above.



  // Use the example functions to avoid a compiler warning about unused functions.

  ftl_ignore_multiple(0, "a", "b");

  ftl_ignore_single(0);

}



}  // namespace android::test