Template class type-specific functions

Question

Ok, so i have this template class, which is kinda like one-way list.

template <typename T> List

and it have this inside function print

public: void Print();

which, as you can guess, prints the list contents from begining to end; However, as template can take classes as T, one can imagine, that i would need different implementations of Print() for that very cases. For example, I have another class Point

class Point{ private: int x, y; public: int getX(); int getY(); }

so i want Print specifically designed for Points. I tried this:

void List<Point>::Print();

but compiler tells me

prototype for void List<Point> Print() doesn match any in class List<Point>

though

candidates are: from List<T> [with T = Point] void List<Point>::Print()

For me it seems like the same fucntion. What's wrong? And how do I write T-specific template class functions?

template<> void List<Point>::Print()

AndyG
– AndyG

2016-11-21 14:06:25 +00:00
Commented Nov 21, 2016 at 14:06 — AndyG
– AndyG, Commented Nov 21, 2016 at 14:06

Hatted Rooster · Accepted Answer · 2016-11-21 14:14:05Z

9

You use explicit template specialization to specialize behaviour of Print for specific types.

For example, for Point:

template <> // No template arguments here ! void List<Point>::Print() // explicitly name what type to specialize { //code for specific Point Print behaviour.. }

answered Nov 21, 2016 at 14:14

Hatted Rooster

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6 Comments

Yury Elburikh Over a year ago

Does it goes in class body? Or outside of it?

Hatted Rooster Over a year ago

@YuryElburikh Outside of it.

Yury Elburikh Over a year ago

now it tells me that "no member function "Print" is declared in List<int>"

Hatted Rooster Over a year ago

@YuryElburikh well an int is not a Point. You should still provide a fallback implementation for Print for the other cases.

Yury Elburikh Over a year ago

And what if i only want Print for ints and Points? I did 'template<> void List<int>::Point();' 'template<> void List<Point>::Print();'

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aspen100 · Accepted Answer · 2016-11-21 14:57:02Z

However, as template can take classes as T, one can imagine, that i would need different implementations of Print() for that very cases

Not at all. You can have a single implementation of Print for every type of object - this is why templates are powerful.

One way to do what you want would be to define the stream operator << in Point, and have a generic Print() method in List. This makes Print available to more than just Point.

More generality ftw.

Hmm, this approach I like a whole lot more, however, for this project I have to use Point provided without any modifications to it

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