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Don't wrap named arg in cref and clarify docs

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This commit is contained in:
Victor Zverovich
2021-03-14 09:08:08 -07:00
parent b8ff3c1820
commit 5a1127b726
3 changed files with 15 additions and 36 deletions
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22
test/core-test.cc
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@@ -469,24 +469,10 @@ TEST(FormatDynArgsTest, NamedStrings) {
TEST(FormatDynArgsTest, NamedArgByRef) {
fmt::dynamic_format_arg_store<fmt::format_context> store;
// Note: fmt::arg() constructs an object which holds a reference
// to its value. It's not an aggregate, so it doesn't extend the
// reference lifetime. As a result, it's a very bad idea passing temporary
// as a named argument value. Only GCC with optimization level >0
// complains about this.
//
// A real life usecase is when you have both name and value alive
// guarantee their lifetime and thus don't want them to be copied into
// storages.
int a1_val{42};
auto a1 = fmt::arg("a1_", a1_val);
store.push_back("abc");
store.push_back(1.5f);
store.push_back(std::cref(a1));
std::string result = fmt::vformat("{a1_} and {} and {} and {}", store);
EXPECT_EQ("42 and abc and 1.5 and 42", result);
char band[] = "Rolling Stones";
store.push_back(fmt::arg("band", std::cref(band)));
band[9] = 'c'; // Changing str affects the output.
EXPECT_EQ(fmt::vformat("{band}", store), "Rolling Scones");
}
TEST(FormatDynArgsTest, NamedCustomFormat) {