Syntax and operators

Spread syntax

You can use spread syntax ('...') in three places:

Function call argument

In function call's arguments. This means to 'spread' the list object here to fill in the positional argument list.

fun someFunc(a, b) {
  print(a + b)
}
var list = [5, 6]
someFunc(...list) // same to 'someFunc(5, 6)'

List literal

In list literal's value list, This means to 'spread' the list object here to fill in the items.

var list = [5, 6];
var ht = [1, 2, ...[3, 4], ...list]; // same to [1, 2, 3, 4, 5, 6]

Struct literal

In struct literal's value list, This means to 'spread' the struct object here to fill in the field.

var name = {
  familyName: 'Hord',
  firstName: 'Luk',
};
var job = 'wood cutter';
var person = {
  ...name,
  age: 23,
};
// same to:
// {
//   familyName: 'Hord',
//   firstName: 'Luk',
//   age: 23,
//   job: 'wood cutter'
// }

Null check syntax

The script is not planning to introduce null safety. However, there are some syntax to help do null check:

var a // a is null
// Nullable member get:
final value = a?.value // value is null and we won't get errors
final result = a?() // nullabla function call
// If null then get another value
final text = a ?? 'hi!' // text is 'hi!'
// If null then assign
a ??= 42
print(a) // a is 42 now

The nullable check will pass to next unary postfix operator like a chain:

var a // a is null
final value = a?.collection[0].value() // value is null and we won't get errors

new

new is a explicit way to call a constructor. Its difference from normal function call is that you can omit the brackets if there's none arguments.

struct P {
  var name = 'Jimmy'
}
final p = new P
print(p)

Operator precedence

Operators in Hetu is a subset of Dart:

Description	Operator	Associativity	Precedence
Unary postfix	e., e?., e++, e--, e1[e2], e()	None	16
Unary prefix	-e, !e, ++e, --e, await e	None	15
Multiplicative	*, /, ~/, %	Left	14
Additive	+,	Left	13
Relational	<, >, <=, >=, as, is, is!, in, in!	None	8
Equality	==, !=	None	7
Logical AND	&&	Left	6
Logical Or	||	Left	5
If null	??	Left	4
Conditional	e1 ? e2 : e3	Right	3
Assignment	=, *=, /=, ~/=, +=, -=, ??=	Right	1