Interfaces and properties

Question

Is it possible to declare a property in an interface without declaring the get- and set-methods for it? Something like:

IValue = interface
  property value: double;
end;

I want to state that the implementor should have a property called value, returning a double, but I really don't care if it returns a private field or the result from a function.

If it is possible, is it possible to declare it read/write or read-only?

when there is so many other reasons to pick from? Actually, I liked Delphi quite much, but it's a closed chapter for me now. — Vegar, Sep 13 '12 at 13:01
@NiyokoYuliawan It's' probably the worst thing I don't like about Delphi (being a Delphi lover since Turbo Pascal 2) — Reversed Engineer, Apr 11 '19 at 11:00

score 41 · Accepted Answer · answered Aug 11 '09 at 13:20

No. Interfaces are implemented as function tables (basically a simple virtual method table) and the compiler needs to know there's a function to map the property onto. You can declare a property on an interface, but it has to have functions as getter/setter values, not fields. You can make it read-only or write-only, though.

score 8 · Answer 2 · answered Aug 11 '09 at 16:46

8

When working with properties in an interface, think of the property as a shortcut to the reader/writer. Only one is required to satisfy the shortcut...otherwise it doesn't point to anything.

answered Aug 11 '09 at 16:46

skamradt

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6

Yep. In fact, the property declaration is purely there for your convenience. If you create an interface with a property on it, and put it on a class that implements the functions but doesn't declare the property, that class will compile just fine. – Mason Wheeler Aug 11 '09 at 16:51

Interfaces and properties

2 Answers2