C++ equals sign in function call?

Question

Reviewing some of the JUCE sample code, I ran across this function call:

Arpeggiator()
{
    addParameter (speed = new AudioParameterFloat ("speed", "Arpeggiator Speed", 0.0, 1.0, 0.5));
}

Is this just an assignment within a function call? Or is there some other kind of c++ magic going on here?

I cannot tell because `=` operator may be overloaded and there are no declaration/definition of `speed` and its type. — MikeCAT, Jun 02 '16 at 16:51
Typically this is used to both assign the value of `speed` and pass this value on to `addParameter()` on the same line. — Havenard, Jun 02 '16 at 16:54
@MikeCAT The `operator=()` can't be overloaded for a `AudioParameterFloat *`. Well, `speed` could be something else, but according conventions the overloaded `operator=()` should return a reference to that instance. — πάντα ῥεῖ, Jun 02 '16 at 16:59

score 6 · Accepted Answer · edited May 23 '17 at 10:28

6

Is this just an assignment within a function call?

Yes.

Or is there some other kind of c++ magic going on here?

Not much magic there, the return value of an assignment operation usually is a reference to the instance assigned.

So it's equivalent to (I suspect that is constructor code):

class Arpeggiator : public Decorator {
public:
     Arpeggiator() {
         speed = new AudioParameterFloat ("speed", "Arpeggiator Speed", 0.0, 1.0, 0.5);
         addParameter (speed); // Probably inherited from Decorator 
     }
private: 
    AudioParameterFloat* speed;
};

As the question came up, what happens if there's an overloaded assignment operator.

As stated in this answer in the canonical Operator overloading:

Assignment Operator

There's a lot to be said about assignment. However, most of it has already been said in GMan's famous Copy-And-Swap FAQ, so I'll skip most of it here, only listing the perfect assignment operator for reference:
X& X::operator=(X rhs)
{
   swap(rhs);
   return *this;
}

edited May 23 '17 at 10:28

Community

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answered Jun 02 '16 at 16:54

πάντα ῥεῖ

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What if the `operator=` is overloaded and it does not return the same thing? – NathanOliver Jun 02 '16 at 16:58
1

@NathanOliver The code will fail then, was that in question at any time? – πάντα ῥεῖ Jun 02 '16 at 17:00
2

@NathanOliver then the library's quite badly designed – coyotte508 Jun 02 '16 at 17:02
On the other hand, it looks like the library's version of a named argument. One could argue that named arguments do not make sense outside of a function call, in which case an error for the extracted assignment would be expected. – chris Jun 02 '16 at 17:10

C++ equals sign in function call?

1 Answers1

Assignment Operator