R help - Aug 2011 - R.oo error upon construction

Hello,

Using the R.oo package, how do I throw an error if a field is not present
when the user of the class creates the object?

Using the example in the R.oo package:

setConstructorS3("Person", function(name, age) {
  if (missing(name)) name <- NA;
  if (missing(age))  age <- NA;

  extend(Object(), "Person",
    .name=name,
    .age=age
  )
})

[rest of class methods here...etc...]

User types this with no issues because both age and name are there:

p1 <- Person("Dalai Lama", 67)

User types this and I want it to throw an error because the age field is
missing:

p1 <- Person("Dalai Lama")

Link to the example I am drawing from:
http://127.0.0.1:22346/library/R.oo/html/Object.html

I know how to throw an error when a method is used. I want to throw an error
when the object is created.

I've tried print and cat statements in the Constructor section and after the
extend statement.

Thanks,
Ben

	[[alternative HTML version deleted]]

Hi,

you can do something like:

setConstructorS3("Person", function(name, age) {
  # Check for missing arguments, but allow for empty
  # constructor calls, i.e. Person().
  if (missing(name) && missing(age)) {
    name <- NA;
    age <- NA;
  } else if (missing(name)) {
    throw("Argument 'name' is missing.");
  } else if (missing(age)) {
    throw("Argument 'age' is missing.");
  }

  extend(Object(), "Person",
    .name=name,
    .age=age
  )
})

/Henrik

On Tue, Aug 9, 2011 at 12:21 AM, Ben qant <ccquant at gmail.com>
wrote:
> Hello,
>
> Using the R.oo package, how do I throw an error if a field is not present
> when the user of the class creates the object?
>
> Using the example in the R.oo package:
>
> setConstructorS3("Person", function(name, age) {
> ?if (missing(name)) name <- NA;
> ?if (missing(age)) ?age <- NA;
>
> ?extend(Object(), "Person",
> ? ?.name=name,
> ? ?.age=age
> ?)
> })
>
> [rest of class methods here...etc...]
>
> User types this with no issues because both age and name are there:
>
> p1 <- Person("Dalai Lama", 67)
>
> User types this and I want it to throw an error because the age field is
> missing:
>
> p1 <- Person("Dalai Lama")
>
> Link to the example I am drawing from:
> http://127.0.0.1:22346/library/R.oo/html/Object.html
>
> I know how to throw an error when a method is used. I want to throw an
error
> when the object is created.
>
> I've tried print and cat statements in the Constructor section and
after the
> extend statement.
>
> Thanks,
> Ben
>
> ? ? ? ?[[alternative HTML version deleted]]
>
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