What do you call this construct?

[joe]

Curious if this type of construct has a name, or is a recognized
design pattern:

class Function
{
public:
Function() { // do loads of work here in the Constructor, store result
in m_result }

operator double() { return m_result;} //Automatic Type Conversion

private:
double m_result;
};

with the expected simple usage:

double value = Function();

Is there some recognized caveat to the above? I don't see it used
very often.

 

[Victor Bazarov]

Curious if this type of construct has a name, or is a recognized
design pattern:

class Function
{
public:
Function() { // do loads of work here in the Constructor, store result
in m_result }

operator double() { return m_result;} //Automatic Type Conversion

private:
double m_result;
};

with the expected simple usage:

double value = Function();

Is there some recognized caveat to the above? I don't see it used
very often.

What's the advantage of that class implementation over, say,

double Function() {
double _result;
// do loads of work here, store the result in _result
return _result;
}

? I don't see any in your code. And the syntax looks pretty much
like a function call, so it would be very confusing to somebody
reading the code to learn that 'Function' is not a function at all.

V

 

[Ian Collins]

Curious if this type of construct has a name, or is a recognized
design pattern:

class Function
{
public:
Function() { // do loads of work here in the Constructor, store result
in m_result }

operator double() { return m_result;} //Automatic Type Conversion

private:
double m_result;
};

with the expected simple usage:

double value = Function();

Is there some recognized caveat to the above? I don't see it used
very often.

I guess it could be called the "abuse of a class" pattern.

 

[Piyo]

I guess it could be called the "abuse of a class" pattern.

You need to add it to the antipattern list since you coined it

http://en.wikipedia.org/wiki/Antipattern

 

[Venkat]

Without going into "it is a bad idea to do", I would refer you to
TCPL, 3rd Ed. S11.4.
It is a way to do type conversion.