Designing an API to accept a generic output stream as a parameter

Question

I am designing an API using the LLVM library which will accept an output stream as one of its constructor parameters. The LLVM coding standards dictate the following:

Use raw_ostream

LLVM includes a lightweight, simple, and efficient stream implementation in llvm/Support/raw_ostream.h, which provides all of the common features of std::ostream. All new code should use raw_ostream instead of ostream.

Unlike std::ostream, raw_ostream is not a template and can be forward declared as class raw_ostream. Public headers should generally not include the raw_ostream header, but use forward declarations and constant references to raw_ostream instances.

I must abide by the LLVM coding standards, so I am trying to accept a raw_ostream as a parameter in my constructor. I have tried passing a raw_ostream by reference and by pointer, but I receive the following error message at compile time:

note: candidate constructor not viable: no known conversion from 'llvm::raw_ostream &()' to 'llvm::raw_ostream &'...

What should my constructor look like to accept a parameter of type 'llvm::raw_ostream &()'? I would like to initialize a class member to this output stream.

Here is my current code:

Constructor

MyClass(raw_ostream &OS) : OutputStream(OS) {}

Caller

MyClass x = new MyClass(&outs);

outs is documented beginning at line 665 of this link

Answer 1

There are tons of examples within the LLVM source where raw_ostream is a function / method argument. It's almost always (..., raw_ostream &OS, ...)

Here's a representative example from CodeGen/AsmPrinter/AsmPrinter.cpp:

static void emitComments(const MachineInstr &MI, raw_ostream &CommentOS) {
  // ... code
}