# 太空飞船操作符（<=>）

## 目录：

* 简介
* 整型比较
* 字符串比较
* 数组比较
* 资料
* usort 场景示例

## 简介：

太空飞船操作符在比较变量时非常有用，这里说的变量包括标量类型（字符串型、整型、浮点型等）、，数组、对象。这个操作符相当于把三个比较符（`== 、 < 、 >`）融合成一个。

比如说使用场景可以用于 usort 、uasort 、uksort 的回调函数。具体使用规则如下：

* 当符号两边相等时返回 0
* 当符号右边大于符号左边时返回 -1
* 当符号左边大于符号右边时返回 1

## 整型比较：

例子：

```php
<?php
$intA = 1;
$intB = 2;
$intC = 1;

echo '整型比较:<br>';

echo $intA <=> $intC; // 返回 0
echo '<br>';

echo $intA <=> $intB; // 返回 -1
echo '<br>';

echo $intB <=> $intC; // 返回 1
```

执行结果：

```
整型比较:
0
-1
1
```

## 字符串比较：

例子：

```php
<?php
echo '字符串比较:<br>';

echo 'PHP 7' <=> 'PHP 7'; //返回 0
echo '<br>';

echo 'a' <=> 'b'; // 返回 -1
echo '<br>';

echo 'z' <=> 'x'; // 返回 1
```

执行结果：

```
字符串比较:
0
-1
1
```

## 数组比较：

```php
<?php
echo '数组比较:<br>';
echo [1,2,3] <=> [1,2,3]; // 0
echo "<br>";
echo [1,2,3] <=> [3,2,1]; // -1
echo "<br>";
echo [3,2,1] <=> [1,2,3]; // 1
```

执行结果：

```
数组比较:
0
-1
1
```

## 对象比较:

```php
<?php
// Objects
$a = (object) ["a" => "b"]; 
$b = (object) ["a" => "b"]; 
echo $a <=> $b; // 0
$a = (object) ["a" => "b"]; 
$b = (object) ["a" => "c"]; 
echo $a <=> $b; // -1
$a = (object) ["a" => "c"]; 
$b = (object) ["a" => "b"]; 
echo $a <=> $b; // 1
$a = (object) ["a" => "b"]; 
$b = (object) ["b" => "b"]; 
echo $a <=> $b; // 0
```

## usort 场景示例：

```php
<?php
// 老的 if 方式比较
function normal_sort($a, $b) : int
{
    if($a == $b) {
        return 0;
    } elseif ($a < $b) {
        return -1;
    } else {
        return 1;
    }
}

// 新的太空飞船操作符比较
function space_sort($a, $b) : int
{
    return $a <=> $b;
}

$normalArray = [1,34,56,67,98,45];

usort($normalArray, 'normal_sort');

foreach($normalArray as $k => $v) {
    echo $k.' => '.$v.'<br>';
}

//SpaceShip example
$sarray = [1,34,56,67,98,45];

usort($sarray, 'space_sort');

foreach($sarray as $key => $value) {
    echo $key.' => '.$value.'<br>';
}
```

以上代码if条件判断比较的方式，采用太空操作符一行搞定！输出结果:

```php
0 => 1
1 => 34
2 => 45
3 => 56
4 => 67
5 => 98
0 => 1
1 => 34
2 => 45
3 => 56
4 => 67
5 => 98
```

## 资料：

[php官方wiki 太空飞船操作符示例](https://wiki.php.net/rfc/combined-comparison-operator)


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