method-introspect.md
In S7: An Object Oriented System Meant to Become a Successor to S3 and S4

method introspection: errors on invalid inputs

Code
  method(print, 1)
Condition
  Error:
  ! `generic` must be a <S7_generic>, not a <closure>
Code
  foo <- new_generic("foo", "x")
  method(foo)
Condition
  Error:
  ! Must supply exactly one of `class` and `object`
Code
  method(foo, 1)
Condition
  Error:
  ! Can't convert `signature` to a valid class. Class specification must be an S7 class object, the result of `new_S3_class()`, an S4 class object, or a base class, not a <double>.
Code
  method(foo, new_union(class_integer, class_double))
Condition
  Error in `as_dispatch()`:
  ! Can't dispatch on unions; must be a concrete type
Code
  foo2 <- new_generic("foo2", c("x", "y"))
  method(foo2, object = list(class_character))
Condition
  Error:
  ! `object` must be length 2

method introspection: errors if no method found

Code
  method(foo, class = class_integer)
Condition
  Error:
  ! Can't find method for `foo(<integer>)`.
Code
  method(foo, object = 1L)
Condition
  Error:
  ! Can't find method for `foo(<integer>)`.
Code
  method(foo2, class = list(class_integer, class_double))
Condition
  Error:
  ! Can't find method for generic `foo(x, y)`:
  - x: <integer>
  - y: <double>
Code
  method(foo2, object = list(1L, 2))
Condition
  Error:
  ! Can't find method for generic `foo(x, y)`:
  - x: <integer>
  - y: <double>

method explanation: shows all possible methods along with matches

   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])