Explain method dispatch

method_explain() shows all possible methods that a call to a generic might use, which ones exist, and which one will actually be called.

Note that method dispatch uses a string representation of each class in the class hierarchy. Each class system uses a slightly different convention to avoid ambiguity.

• S7: pkg::class or class

• S4: S4/pkg::class or S4/class

• S3: class

method_explain(generic, class = NULL, object = NULL)

Arguments

generic

A generic function, i.e. an S7 generic, an external generic, an S3 generic, or an S4 generic.

class, object

Perform introspection either with a class (processed with as_class()) or a concrete object. If generic uses multiple dispatch then both object and class must be a list of classes/objects.

Value

Nothing; this function is called for it's side effects.

Examples

Foo1 <- new_class("Foo1")
Foo2 <- new_class("Foo2", Foo1)

add <- new_generic("add", c("x", "y"))
method(add, list(Foo2, Foo1)) <- function(x, y) c(2, 1)
method(add, list(Foo1, Foo1)) <- function(x, y) c(1, 1)

method_explain(add, list(Foo2, Foo2))
#>    add([Foo2], [Foo2])
#> -> add([Foo2], [Foo1])
#>    add([Foo2], [S7_object])
#>    add([Foo2], [ANY])
#>    add([Foo1], [Foo2])
#> *  add([Foo1], [Foo1])
#>    add([Foo1], [S7_object])
#>    add([Foo1], [ANY])
#>    add([S7_object], [Foo2])
#>    add([S7_object], [Foo1])
#>    add([S7_object], [S7_object])
#>    add([S7_object], [ANY])
#>    add([ANY], [Foo2])
#>    add([ANY], [Foo1])
#>    add([ANY], [S7_object])
#>    add([ANY], [ANY])