Dart有如下操作符：

在操作符表中，优先级是从上到下递减。例如，即便&&在之前，优先级是求余（%）>判断相等（）> 且(&&)。下面代码中，计算顺序是一致的

// Parentheses improve readability.
if ((n % i == 0) && (d % i == 0)) ...

// Harder to read, but equivalent.
if (n % i == 0 && d % i == 0) ...

注意：操作符左右各有一个对象，操作符具体行为是由左边的对象决定的，这个涉及到操作符重载，比如Vector和Point对象重载了+号操作符的行为，Vector+Point的+号具体行为由Vector决定。

Arithmetic operators 算术运算符

Dart supports the usual arithmetic operators, as shown in the following table.
Dart支持常见的几种算术运算符

assert(2 + 3 == 5);
assert(2 - 3 == -1);
assert(2 * 3 == 6);
assert(5 / 2 == 2.5); // Result is a double
assert(5 ~/ 2 == 2); // Result is an int
assert(5 % 2 == 1); // Remainder

assert('5/2 = ${5 ~/ 2} r ${5 % 2}' == '5/2 = 2 r 1');

Dart也支持自增自减运算符

var a, b;

a = 0;
b = ++a; // Increment a before b gets its value.
assert(a == b); // 1 == 1

Equality and relational operators 关系运算符

| Greater than
<| Less than
=| Greater than or equal to
<=| Less than or equal to

验证两个对象是否相同，用操作符,（在极少数情况下，你要判断两个对象是否完全相同，需要用identical()函数）
下面是的判断逻辑：
步骤1.如果x,y都是null,返回true ,x,y只有一个是null,返回false
步骤2.返回x.(y)的结果，这种写法类似a.method(params),可以将看做x的方法。

assert(2 == 2);
assert(2 != 3);
assert(3 > 2);
assert(2 < 3);
assert(3 >= 3);
assert(2 <= 3);
a = 0;
b = a++; // Increment a AFTER b gets its value.
assert(a != b); // 1 != 0
a = 0;
b = --a; // Decrement a before b gets its value.
assert(a == b); // -1 == -1

a = 0;
b = a--; // Decrement a AFTER b gets its value.
assert(a != b); // -1 != 0

Type test operators 类操作符

if (emp is Person) {
  // Type check
  emp.firstName = 'Bob';
}

这是上面的简化写法，如果emp是null或者不是Person类型，后续代码不会执行

(emp as Person).firstName = 'Bob';

Assignment operators 赋值运算符

As you’ve already seen, you can assign values using the = operator. To assign only if the assigned-to variable is null, use the ??= operator.
如你所知，可以用=进行赋值，如果只对空对象赋值，可以用??=。

// Assign value to a
a = value;
// Assign value to b if b is null; otherwise, b stays the same
b ??= value;

组合赋值操作符：
= |–= |/= |%= |>>= |^=
+= |*= |~/= |<<= |&=| ||=

等效说明：

var a = 2; // Assign using =
a *= 3; // Assign and multiply: a = a * 3
assert(a == 6);
```

### Logical operators 逻辑运算符

|Operator|	Meaning|
|--|--|
!expr	|inverts the following expression (changes false to true, and vice versa)
||	|logical OR
&&	|logical AND

下面是逻辑运算符示例：
···

if (!done && (col == 0 || col == 3)) {
  // ...Do something...
}

···

### Bitwise and shift operators 位和移位操作符

你可以对数值进行移位操作

Operator|	Meaning
--|--
|&|	AND
\||	OR
^|	XOR
~expr|	Unary bitwise complement (0s become 1s; 1s become 0s)
<<|	Shift left
>>|	Shift right

下面是移位操作示例：
```
final value = 0x22;
final bitmask = 0x0f;

assert((value & bitmask) == 0x02); // AND
assert((value & ~bitmask) == 0x20); // AND NOT
assert((value | bitmask) == 0x2f); // OR
assert((value ^ bitmask) == 0x2d); // XOR
assert((value << 4) == 0x220); // Shift left
assert((value >> 4) == 0x02); // Shift right
```
### Conditional expressions 条件表达式

Dart有两种条件表达式写法，来取代if逻辑。

```
condition ? expr1 : expr2
```
如果condition是true,返回expr1,否则返回expr2
```
expr1 ?? expr2
```
如果expr1不是null,返回expr1,否则返回expr2.
```
var visibility = isPublic ? 'public' : 'private';

String playerName(String name) => name ?? 'Guest';
```

```
// Slightly longer version uses ?: operator.
String playerName(String name) => name != null ? name : 'Guest';
// Very long version uses if-else statement.
String playerName(String name) {
  if (name != null) {
    return name;
  } else {
    return 'Guest';
  }
}
```

### Cascade notation (..) 链式调用操作符
链式操作符允许你对相同对象进行多次调用而不用多次写对象名。

```
querySelector('#confirm') // Get an object.
  ..text = 'Confirm' // Use its members.
  ..classes.add('important')
  ..onClick.listen((e) => window.alert('Confirmed!'));
```

上面的示例等效于：
```
var button = querySelector('#confirm');
button.text = 'Confirm';
button.classes.add('important');
button.onClick.listen((e) => window.alert('Confirmed!'));
```
You can also nest your cascades. For example:
```
final addressBook = (AddressBookBuilder()
      ..name = 'jenny'
      ..email = '[email protected]'
      ..phone = (PhoneNumberBuilder()
            ..number = '415-555-0100'
            ..label = 'home')
          .build())
    .build();
```
注意，链式调用必须由对象发起，比如下面的write返回值为void,所以无法使用链式调用。
```
var sb = StringBuffer();
sb.write('foo')
  ..write('bar'); // Error: method 'write' isn't defined for 'void'.
```

### Other operators 其它操作符


Operator|	Name|	Meaning
--|--|--
()	|Function application|	Represents a function call
[]	|List access	|Refers to the value at the specified index in the list
.	|Member access	|Refers to a property of an expression; example: foo.bar selects property bar from expression foo
?.	|Conditional |member access	Like ., but the leftmost operand can be null; example: foo?.bar selects property bar from expression foo unless foo is null (in which case the value of foo?.bar is null)

第四篇准备翻译 Control flow statements 流程控制