fmt_make_format_args_from_map

Summary: A helper function to make an object of format-args type suitable for passing to `fmt::vformat` from an input map.

Reviewed By: Gownta

Differential Revision: D67314712

fbshipit-source-id: 60fef13adc8b946917cbca7ffc5fbf3dffae882b

CMakeLists.txt

@@ -1104,6 +1104,7 @@ if (BUILD_TESTS OR BUILD_BENCHMARKS)
       BENCHMARK fingerprint_benchmark SOURCES FingerprintBenchmark.cpp
       TEST fingerprint_test SOURCES FingerprintTest.cpp
       TEST fixed_string_test SOURCES FixedStringTest.cpp
+      TEST fmt_utility_test SOURCES FmtUtilityTest.cpp
       TEST format_other_test SOURCES FormatOtherTest.cpp
       BENCHMARK format_benchmark SOURCES FormatBenchmark.cpp
       TEST format_test SOURCES FormatTest.cpp

folly/BUCK

@@ -566,6 +566,17 @@ cpp_library(
     ],
 )
 
+cpp_library(
+    name = "fmt_utility",
+    headers = [
+        "FmtUtility.h",
+    ],
+    exported_deps = [
+        "fbsource//third-party/fmt:fmt",
+        ":cpp_attributes",
+    ],
+)
+
 cpp_library(
     name = "format",
     srcs = [

folly/FmtUtility.h

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * 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
+
+#include <fmt/args.h>
+
+#include <folly/CppAttributes.h>
+
+namespace folly {
+
+/// fmt_make_format_args_from_map_fn
+/// fmt_make_format_args_from_map
+///
+/// A helper function-object type and variable for making a format-args object
+/// from a map.
+///
+/// May be useful for transitioning from legacy folly::svformat to fmt::vformat.
+struct fmt_make_format_args_from_map_fn {
+  template <typename Map>
+  fmt::dynamic_format_arg_store<fmt::format_context> operator()(
+      [[FOLLY_ATTR_CLANG_LIFETIMEBOUND]] Map const& map) const {
+    fmt::dynamic_format_arg_store<fmt::format_context> ret;
+    ret.reserve(map.size(), map.size());
+    for (auto const& [key, val] : map) {
+      ret.push_back(fmt::arg(key.c_str(), std::cref(val)));
+    }
+    return ret;
+  }
+};
+inline constexpr fmt_make_format_args_from_map_fn
+    fmt_make_format_args_from_map{};
+
+} // namespace folly

folly/test/BUCK

@@ -704,6 +704,14 @@ cpp_unittest(
     ],
 )
 
+cpp_unittest(
+    name = "fmt_utility_test",
+    srcs = ["FmtUtilityTest.cpp"],
+    deps = [
+        "//folly:fmt_utility",
+    ],
+)
+
 cpp_benchmark(
     name = "format_benchmark",
     srcs = ["FormatBenchmark.cpp"],

folly/test/FmtUtilityTest.cpp

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * 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 <folly/FmtUtility.h>
+
+#include <map>
+#include <string>
+#include <string_view>
+
+#include <gtest/gtest.h>
+
+using namespace std::literals;
+
+struct FmtUtilityTest : testing::Test {};
+
+TEST_F(FmtUtilityTest, fmt_make_format_args_from_map_fn) {
+  EXPECT_EQ(
+      "hello bob you silly goose",
+      fmt::vformat(
+          "hello {name} you {adj} goose",
+          folly::fmt_make_format_args_from_map(
+              std::map<std::string, std::string_view>{
+                  {"name"s, "bob"sv},
+                  {"adj"s, "silly"sv},
+              })));
+}