尝试更好地理解每周提示 #42：通过使用标准模板库复制示例，更喜欢使用工厂函数而不是初始化方法。OP 提供了示例代码：
// foo.h
class Foo {
public:
// Factory method: creates and returns a Foo.
// May return null on failure.
static std::unique_ptr<Foo> Create();
// Foo is not copyable.
Foo(const Foo&) = delete;
Foo& operator=(const Foo&) = delete;
private:
// Clients can't invoke the constructor directly.
Foo();
};
// foo.c
std::unique_ptr<Foo> Foo::Create() {
// Note that since Foo's constructor is private, we have to use new.
return absl::WrapUnique(new Foo());
}
在尝试复制示例时，我在本foo.c节中使用了不同的方法：
std::unique_ptr<Foo> Foo::Create() {
// Attempt to create using std::unique_ptr instead of absl::WrapUnique
return std::unique_ptr<Foo>(new Foo());
}
使用以下命令编译会导致链接器命令失败
$ clang++ -g -Wall -std=c++11 -fsanitize=address foo.cc -o Foo
Undefined symbols for architecture arm64:
"Foo::Foo()", referenced from:
Foo::Create() in robots-cda3fd.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
想我在这里缺少什么？谢谢！