In Go I use := for short variable declaration and = for assignment. How does EK9 handle this?

← Getting Started · Ref: Q1005

EK9 separates declaration from assignment just like Go, but with different symbols.

Go: name := "Steve" short declaration (creates variable)
EK9: name <- "Steve" declaration (creates variable)

Go: name = "Alice" assignment (updates variable)
EK9: name := "Alice" assignment (updates variable)

Notice the swap: Go's := (declare) maps to EK9's <- (declare). Go's = (assign) maps to EK9's := (assign).

EK9 also has : and = as aliases for :=

  name := "Alice"     assignment
  name: "Alice"       same thing
  name = "Alice"      same thing

And :=? for guarded assignment (like Go's 'if err != nil' pattern):

  fallback :=? "default"     only assigns if fallback is currently unset

Go's 'if err := f(); err != nil' pattern becomes an EK9 guard:

  if result <- doSomething()
    useResult(result)

Example

defines module qa.gettingstarted.fromgodeclaration

  defines program

    FromGoDeclarationDemo()
      stdout <- Stdout()

      // Like Go: name := "Steve" (short declaration)
      name <- "Steve"
      stdout.println(name)

      // Like Go: name = "Alice" (assignment)
      name := "Alice"
      stdout.println(name)

      // Like Go: if err := f(); err != nil { ... }
      if greeting <- greetUser(name)
        stdout.println(greeting)

  defines function

    greetUser() as pure
      -> userName as String
      <- rtn as String: "Welcome, " + userName

Common mistakes

E50001 — In EK9, <- declares (like Go's :=) and := assigns (like Go's =). Using := before <- means the variable does not exist yet.

Incorrect:

      name := "Steve"
      name = "Alice"

Correct:

      name <- "Steve"
      stdout.println(name)

Coming from another language?

Go developers: your := becomes EK9's <-, your = becomes EK9's :=. The separation of declaration from assignment is the same concept, different symbols.

Keywords: assignment, go, migration, golang, short variable, declaration