Define a class union — new

A class union represents a list of possible classes. You can create it with new_union(a, b, c) or a | b | c. Unions can be used in two places:

To allow a property to be one of a set of classes, new_property(class_integer | Range). The default default value for the property will be the constructor of the first object in the union. This means if you want to create an "optional" property (i.e. one that can be NULL or of a specified type), you'll need to write (e.g.) NULL | class_integer.
As a convenient short-hand to define methods for multiple classes. method(foo, X | Y) <- f is short-hand for method(foo, X) <- f; method(foo, Y) <- foo

S7 includes built-in unions for "numeric" (integer and double vectors), "atomic" (logical, numeric, complex, character, and raw vectors) and "vector" (atomic vectors, lists, and expressions).

Usage

new_union(...)

Arguments

...: The classes to include in the union. See as_class() for details.

Value

An S7 union, i.e. a list with class S7_union.

Examples

logical_or_character <- new_union(class_logical, class_character)
logical_or_character
#> <S7_union>: <logical> or <character>
# or with shortcut syntax
logical_or_character <- class_logical | class_character

Foo <- new_class("Foo", properties = list(x = logical_or_character))
Foo(x = TRUE)
#> <Foo>
#>  @ x: logi TRUE
Foo(x = letters[1:5])
#> <Foo>
#>  @ x: chr [1:5] "a" "b" "c" "d" "e"
try(Foo(1:3))
#> Error : <Foo> object properties are invalid:
#> - @x must be <logical> or <character>, not <integer>

bar <- new_generic("bar", "x")
# Use built-in union
method(bar, class_atomic) <- function(x) "Hi!"
bar
#> <S7_generic> bar(x, ...) with 6 methods:
#> 1: method(bar, class_integer)
#> 2: method(bar, class_complex)
#> 3: method(bar, class_double)
#> 4: method(bar, class_character)
#> 5: method(bar, class_logical)
#> 6: method(bar, class_raw)
bar(TRUE)
#> [1] "Hi!"
bar(letters)
#> [1] "Hi!"
try(bar(NULL))
#> Error : Can't find method for `bar(<NULL>)`.