2.4 Named arguments

Some methods take a lot of arguments of which you generally only want to specify a few. A good example is the creation of a style object. A style is an object used to control the attributes of displayed text: font, fore- and background colour, underline, etc. Its ->initialise method, serving the same role the constructor in C++, takes 7 arguments. Both calls below create a style object representing an underlined text-fragment:

1 ?- new(X, style(@default, @default, @default, @default, @on)).
2 ?- new(X, style(underline := @on)).

The names of arguments are specified in the reference manual. For example, the method `area->set', used to set one or more of the X-, Y-, H- and W-attributes of a rectangle, has the specification given below. For each argument that is specified as @default, the corresponding slot will not be changed.

area->set: x=[int], y=[int], width=[int], height=[int]

The following example illustrates the usage of this method:

1 ?- new(A, area),
     send(A, set(y := 10, height := 50)).