Created
May 1, 2019 03:30
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Phantom Builder
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#!/usr/bin/env ocaml | |
#use "topfind" | |
#thread | |
#require "core" | |
open Core | |
type name_unset | |
type name_set | |
type age_unset | |
type age_set | |
type t = { | |
name : string ; | |
age : int ; | |
} | |
module Builder : sig | |
type ('name, 'age) b | |
val empty : (name_unset, age_unset) b | |
val set_name : ('name, 'age) b -> name:string -> (name_set, 'age) b | |
val set_age : ('name, 'age) b -> age:int -> ('name, age_set) b | |
val build : (name_set, age_set) b -> t | |
end = | |
struct | |
type ('name, 'age) b = { | |
name : string option ; | |
age : int option ; | |
} | |
let empty = { | |
name = None ; | |
age = None ; | |
} | |
let set_name b ~name = { | |
b with | |
name = Some name | |
} | |
let set_age b ~age = { | |
b with | |
age = Some age | |
} | |
let build b : t = | |
{ | |
name = Option.value_exn b.name ; | |
age = Option.value_exn b.age ; | |
} | |
end | |
let () = | |
let b = Builder.empty | |
|> Builder.set_age ~age:27 | |
|> Builder.set_name ~name:"John Cena" in | |
let built = Builder.build b in | |
print_endline built.name |
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