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.

function 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)

delete operator

The delete keyword removes a variable, struct member, or subscript value. Three modes are available:

Delete a local variable

Removes a top-level or local variable from its namespace. Subsequent access throws an undefined error.

var a = 42
delete a
print(a) // Error: a is undefined

Delete a struct member

Removes a field from a struct object. The memberGet access pattern is used.

var obj = { name: 'the world', meaning: 42 }
delete obj.meaning
print(obj) // { name: 'the world' }

Delete a subscript value

Removes a key from a map or a field from a struct by subscript key.

var map = { 'a': 1, 'b': 2 }
delete map['a']
print(map) // { b: 2 }

var obj = { name: 'test', meaning: 42 }
delete obj['meaning']
print(obj) // { name: 'test' }

Notes:

• Deleting a local variable removes it from the namespace entirely.
• You cannot delete fields defined on a class instance.
• delete list[index] is not supported for List objects.

Operator precedence

Operators in Hetu is a subset of Dart: