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Subclass a struct

Source: R/struct.R
extend.Rd

The child gets the parent's fields plus its own, inherits the parent's class – so it is accepted wherever the parent is – and may retype a parent field by repeating its name.

Usage

extend(.parent, ...)

Arguments

.parent

The struct to extend, or an S7 class.

...

The subclass's name as the single unnamed string, then extra or replacement fields.

Value

A constructor of class typed_struct.

See also

struct(), partial()

Examples

Animal <- struct("Animal", name = chr[1], legs = int[1] %default% 4L)
Bird <- extend(Animal, "Bird", can_fly = lgl[1])

tweety <- Bird(name = "Tweety", legs = 2, can_fly = TRUE)
tweety
#> <Bird>
#>   name    : "Tweety"
#>   legs    : 2L
#>   can_fly : TRUE
inherits(tweety, "Animal")
#> [1] TRUE
is_valid(Animal, tweety)
#> [1] TRUE

# a child may retype a parent field
fields(extend(Animal, "Centipede", legs = int[1][. > 50]))
#> [1] "name" "legs"