Parameters

Added by dholton dholton

Parameters are the objects you can pass to Functions, Closures, or Callable Types which handle Events.

A parameter is declared with a name, followed by "as", followed by the type: paramname as type. If there is no "as type", then the type is assumed to be type object. Examples Method/Function example

def mymethod(x as int, y as long): ...

Closure

c = def(z): print z

obj = "a string" c(obj)

Callable Type + Event

import System

class Sandwich: event Eating as EatingEvent callable EatingEvent(sammich as object, type as string)

def Eat():
	Eating(self, "Turkey sammich.")

turkeyAndSwiss = Sandwich() turkeyAndSwiss.Eating += def(obj, sammich): print "You're eating a $sammich! It must be good." turkeyAndSwiss.Eat()

Variable number of parameters

Boo allows you to call or declare methods that accept a variable (unknown) number of parameters.

You add an asterix (*) before the parameter name to signify that it holds multiple parameter values. If there is no 'as type', the type is assumed to be an array of objects: (object). You can declare the type as any array type. For example (int) if your method only accepts int parameters.

Here is an example:

def mymethod(x as int, *rest): print "first arg:", x for item in rest: print "extra param:", item print

mymethod(1, "a", "b", "c") mymethod(2, 3, 4, 5, 6, 7)

Some boo builtins accept a variable number of parameters, like matrix() and ICallable.Call. ByRef parameters

Add a "ref" keyword before the parameter name to make a parameter be passed by reference instead of by value. This allows you to change a variable's value outside of the context where it is being used. Some examples: Basic byref example:

def dobyref(ref x as int): x = 4

x = 1 print x //-->1 dobyref(x) print x //-->4

DllImport example:

Wrapping a native method that takes a parameter by reference.

import System.Windows.Forms from System.Windows.Forms import System.Drawing from System.Drawing import System.Runtime.InteropServices

class ExtTextBox(TextBox): //must be static [DllImport("user32")] static def GetCaretPos(ref p as Point): pass

f = Form(Text: "byref test") t = ExtTextBox() f.Controls.Add(t)

b = Button(Text: "GetCaretPos") b.Click += do: p = Point(0,0) t.GetCaretPos(p) MessageBox.Show(p.X.ToString()) b.Location = Point(0,100) f.Controls.Add(b) Application.Run(f)

See also tests/testcases/integration/byref*.boo in the boo source distribution.