Is there a specific term for an accessor method that returns a boolean value?

Question

I seem to recall that there is a specific term for an accessor method that returns a Boolean value but it escapes me. For example: typical methods such as:

class Example {
    bool isDirty();
    bool hasChildren();
    bool isValid(SomeType obj);
};

I will also settle for such a term as applied to a non-member functions.

Answer 1

A function from some type T to Boolean is usually called a predicate, and if you want to make clear that it is a method of an object, i.e. that it takes the implicit this argument in addition to its other arguments, then you could call it a predicate method. If it takes no other arguments except the implicit this argument, then you can call it a predicate property.

See for example Predicate<T> in .NET and e.g. javax.sql.rowset.Predicate or com.google.common.base.Predicate in Java.

Answer 2

If the method is simply returning an attribute of the object, I would call it an accessor, since it is simply used to access a private member variable of the object.

If the method performs some kind of computation or contains logic (beyond the possibility of logging or validation), it's simply a method. It's no different than a method that performs any other operations that use the state of the object and return a value that's not a boolean.

If the method preforms some special task, such as checking equality or validity, I might want to refer to it by what it does, such as calling it a "validator method" or "equality method". Those names is a bit shorter than saying "a method that checks the validity of the object" or "a method that checks the equality of this object against another".

Not everything has a special name, though. Call it by what it is.

Answer 3

A switch (which is ambiguous), a flag, a bool, a state... Nothing I can think of is specific to a getter...

Different environments have different conventions...

Ruby: some_object.is_something?

ObjC: [someObject isSomething]

So I guess I support the "is doctrine"...