c++ - Returning *this in member functions

Question

I recently used a library that allows the following type of syntax:

MyClass myObject;
myObject
    .setMember1("string value")
    .setMember2(4.0f)
    .setMember3(-1);

Obviously this is accomplished by having the setters return a MyClass & type; something like return *this. I like the way this code looks, but I don't see it a lot. When that happens I'm usually suspicious as to why.

So, is this a bad practice? What are some of the implications of doing it like this?

Answer 1

This is sometimes referred to as the Named Parameter Idiom or method chaining. This isn't bad practice, it can aid readability. Consider this example lifted from the C++ FAQ

File f = OpenFile("foo.txt")
            .readonly()
            .createIfNotExist()
            .appendWhenWriting()
            .blockSize(1024)
            .unbuffered()
            .exclusiveAccess();

The alternative would be to use positional arguments to the OpenFile method, requiring the programmer to remember the position of each argument.