CODEWITHSUNDEEP
stringprintfocaml
laifs
laifs

Reputation: 329

OCaml: Converting strings to ('a, unit, string) format?

I need to convert from a string to a format. I'm given an array of formats, and I would like access each format and use sprintf on them.

e.g.

let errors = [| "format 1"; "format 2"; ... ; "format 512" |]
let code_to_string (error_code : int) :(string) = sprintf errors.(error_code)

I saw this question. According to the best answer, different strings produce formats of different types, which is why this:

let errors = [| format_of_string "format 1"; 
                format_of_string "format 2"; 
                ...
                format_of_string "format 512" |]

doesn't work.

Is there a way to store all formats as strings, and then convert them when needed? Or would I have to write a function for each of the strings? e.g.

let error1 = sprintf "format 1" args
let error2 = sprintf "format 1" args
...
let error512 = sprintf "format 512" args

Upvotes: 4

Views: 1247

Answers (1)

ivg
ivg

Reputation: 35210

You can convert arbitrary statically unknown values of type string into values of type format6 using Scanf.format_from_string. But, of course, you need to know the type of the format (and they all should unify).

Here is the motivating example:

# let fmt = Scanf.format_from_string "Hello: %d" "%d";;
val fmt : (int -> '_a, '_b, '_c, '_d, '_d, '_a) format6 = <abstr>
# Printf.printf fmt 12;;
Hello: 12- : unit = ()

P.S. And here is a more extreme use of this feature.

Upvotes: 3

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