Which types are allowed for typed program arguments in EK9?

← Syntax and Structure Rules · Ref: Q947

Program arguments support the built-in types listed below (String, Integer, Float, Boolean, Character and more). NOT custom types.

EK9 programs with typed parameters (style 2) can only use types that the runtime can parse from command-line strings. Custom classes, records, and complex types cannot be automatically parsed.

SUPPORTED TYPES

String, Integer, Float, Boolean, Character, Bits, Date, Time, DateTime, Duration, Millisecond, Colour, Resolution, Dimension, Money and RegEx.

UNSUPPORTED (E07600)

Custom classes, records, traits, enumerations, Dict, Optional, Path, GUID, or any user-defined type. (A List is only accepted as the single List of String parameter of style 1.)

WORKAROUND

Use String parameters and parse manually:

  defines program
    MyProgram()
      -> configPath as String
      stdout <- Stdout()
      stdout.println(`Parse ${configPath} into your custom type`)

See Q889 for program argument styles. See Q888 for program return type.

Example

defines module qa.syntax.programargtypes

  defines program

    <?-
      Program with typed arguments.
      Only built-in parseable types are allowed.
    -?>
    ProgramArgumentTypesDemo()
      ->
        name as String
        age as Integer
        verbose as Boolean

      stdout <- Stdout()
      stdout.println(`Name: ${name}`)
      stdout.println(`Age: ${age}`)
      stdout.println(`Verbose: ${verbose}`)

Common mistakes

E07600 — Program arguments are limited to a finite set of parseable built-in types; GUID (like any custom or unsupported type) is rejected with E07600 - use String and parse manually. See ek9 -h E07600 for details.

Incorrect:

        name as GUID

Correct:

        name as String

Coming from another language?

Java: main(String[]) only. Python: sys.argv strings. Go: os.Args strings. Rust: std::env::args strings. EK9: compiler-parsed typed parameters from built-in parseable types only.

Keywords: Boolean, argument, Integer, E07600, custom, String, type, Float, program, supported