Lexical

Keywords

The reserved words, the contextual words that are ordinary identifiers elsewhere, and the keywords that may still name members.

since 0.1.0-alpha.1linuxwindowswasm

Description

A keyword is a word the language reserves for its own syntax. These words cannot be used as the name of a variable, parameter, class or function:

namespace  class  struct  enum  interface  public  private  new  mutating
distinct  const  readonly  weak  get  set  return  var  let  await  bind
inject  use  uses  if  else  while  for  in  match  is  this  true  false
break  continue  do  using  try  catch  throw

The built-in type names int, string, bool, float, char, byte, void and the other sized numeric types are not keywords. They are ordinary names that resolve to declarations in the standard library.

attribute, comptime, rule, macro, as and override are contextual keywords. They have a meaning only where a declaration, a use ... as ... import or (for override) a class member expects them. Everywhere else they are ordinary identifiers.

Nine keywords can also be used as the name of a member: get, set, is, in, use, uses, new, bind and inject. A class may declare a field or method with one of those names, and object.name reaches it. Their keyword meaning applies only at the start of a statement or declaration.

Keywords as member names

class Switch {
    bool is = true;
    int in = 3;
    int use() => 4;
    string bind() => "bound";
    int get() => 5;
}
Switch s = Switch();
console.writeln(s.is);
console.writeln(s.in);
console.writeln(s.use());
console.writeln(s.bind());
console.writeln(s.get());

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true
3
4
bound
5

Rules

A word in the keyword list cannot be a variable, parameter, class, function or namespace name.
Of those, get, set, is, in, use, uses, new, bind and inject are accepted as the name of a field or method and after .. Every other keyword is rejected there.
attribute, comptime, rule, macro, as and override are ordinary identifiers outside their declaration positions, so int rule = 3; is legal. override is a modifier only in member position, where a member can start after it (lang.override); int override = 6; is an ordinary variable.
int, string, bool, float, char, byte and the other primitive names are identifiers, not keywords.

Examples

Contextual keywords as ordinary names, and a keyword as a member name:

int attribute = 1;
int comptime = 2;
int rule = 3;
int macro = 4;
int as = 5;
int override = 6;

class Registry {
    int get(int key) => key;
    int set = 0;
    int new = 1;
    int override = 2;
}

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Notes

readonly and weak are reserved even though they appear only in a few declarations.