php - 运算符 <=> 如何比较对象？

标签 php php-7 spaceship-operator

在给出这个例子的 RFC 中:

// only values are compared
$a = (object) ["a" => "b"]; 
$b = (object) ["b" => "b"]; 
echo $a <=> $b; // 0


但是当我执行它时，我得到 1 作为输出:
$a = (object) ["a" => "b"];
$b = (object) ["b" => "b"];
echo $a <=> $b; //1

我现在不明白 <=> 如何比较对象？在 RFC 中，它说它仅按值进行比较。

附言我在 vagrant 下使用 PHP 7.0.4-6+deb.sury.org~trusty+1 (cli) ( NTS )

更新:
php > echo (object)["b"=>"b"] <=> (object)["b"=>"b"];
0
php > echo (object)["b"=>"b"] <=> (object)["a"=>"b"];
1
php > echo (object)["a"=>"b"] <=> (object)["b"=>"b"];
1

最佳答案

在阅读 RFC 时，我们发现它自相矛盾:

Add a new operator (expr) <=> (expr), it returns 0 if both operands are equal, 1 if the left is greater, and -1 if the right is greater. It uses exactly the same comparison rules as used by our existing comparison operators: <, <=, ==, >= and >. (See the manual for details)



注意: 参见 == ，这意味着飞船运算符(operator)做了一个松散的比较。

稍后在示例中:

// only values are compared
$a = (object) ["a" => "b"]; 
$b = (object) ["b" => "b"]; 
echo $a  $b; // 0


飞船操作符只是操作符 < 、 == 和 > 的组合。它根据它的评估结果给出各自的返回值:
operator(s):   <  =  >
return value: -1  0  1

现在 arrays 和 objects 有点复杂 types 。要了解 <=> PHP spaceship 运算符的作用，我们需要查看并了解 < 、 == 和 > 对数组和对象的作用。

因此，让我们看看每种类型的比较运算符 < 、 > 、 == 。首先我们将查看 < 和 > ，然后我们还将查看 == 。

数组比较运算符

现在，对于数组 < 和 > 已记录 here :

┌───────────┬───────────┬──────────────────────────────────────────────────┐
│ type of   │ type of   │                                                  │
│ Operand 1 │ Operand 2 │ Result                                           │
├───────────┼───────────┼──────────────────────────────────────────────────┤
│ array     │ array     │ Array with fewer members is smaller,             │
│           │           │ if key from operand 1 is not found in operand 2  │
│           │           │ then arrays are uncomparable,                    │
│           │           │ otherwise - compare value by value               │
└───────────┴───────────┴──────────────────────────────────────────────────┘


这也可以用 code 来写和表示:

Example #2 Transcription of standard array comparison

<?php
// Arrays are compared like this with standard comparison operators
function standard_array_compare($op1, $op2)
{
    if (count($op1) < count($op2)) {
        return -1; // $op1 < $op2
    } elseif (count($op1) > count($op2)) {
        return 1; // $op1 > $op2
    }
    foreach ($op1 as $key => $val) {
        if (!array_key_exists($key, $op2)) {
            return null; // uncomparable
        } elseif ($val < $op2[$key]) {
            return -1;
        } elseif ($val > $op2[$key]) {
            return 1;
        }
    }
    return 0; // $op1 == $op2
}
?>


我们可以通过一些测试轻松地测试这一点。使用 methods like in math 并且总是只改变一件事，所以我们可以确保我们在这里是正确的:

/**
/*
/* Testing operators: < and >
/*
 */ 

//Test case
//Variations: amount, values and keys (order)
//Test count: 9
//    Failed: 0
//    Passed: 9    
{
    //Test case 1.1
    $a = [1];
    $b = [1];

    //Passed
    var_dump("Same amount of elements, keys and values: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
   
    //Test case 1.2
    $a = [1];
    $b = [1, 1];

    //Passed
    var_dump("NOT same amount of elements, but same values: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));

    //Test case 1.3 
    $a = [10];
    $b = [1, 1];

    //Passed
    var_dump("NOT same amount of elements nor values: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
    
    //Test case 1.4
    $a = [1 => 1];
    $b = [10 => 1];

    //Passed
    var_dump("Same amount of element and values, NOT same keys: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));

    //Test case 1.5
    $a = [10];
    $b = [1];

    //Passed
    var_dump("Same amount of elements and keys, NOT same values: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
    
    //Test case 1.6
    $a = [1 => 1, 2 => 1];
    $b = [2 => 1, 1 => 1];

    //Passed
    var_dump("Same amount of elements and keys in different order: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
    
    //Test case 1.7
    $a = [1 => 1, 2 => 5];
    $b = [2 => 5];

    //Passed
    var_dump("Same values, NOT same amount of elements nor keys: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
    
    //Test case 1.8
    $a = [10 => 1];
    $b = [1 => 10];

    //Passed
    var_dump("NOT same keys nor values: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
    
    //Test case 1.9
    $a = [1 => 1, 2 => 1];
    $b = [2 => 10, 1 => 1];

    //Passed
    var_dump("Same amount of elements and values, NOT same keys nor order: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
    
}


echo PHP_EOL . PHP_EOL . PHP_EOL;  //Test case separator

/**
/*
/* Test case end
/*
 */

//NULL, TRUE, FALSE 2 str func
function bool2str($v){if($v === NULL)return "NULL";elseif($v === FALSE)return "FALSE";elseif($v === TRUE)return "TRUE";else return "UNEXPECTED: '$v'";}


对于相等/恒等运算符 == 和 === 我们找到了数组 here 的文档:

┌───────────┬──────────┬──────────────────────────────────────────────────┐
│ Example   │ Name     │ Result                                           │
├───────────┼──────────┼──────────────────────────────────────────────────┤
│ $a == $b  │ Equality │ TRUE if $a and $b have the same key/value pairs. │
│ $a === $b │ Identity │ TRUE if $a and $b have the same key/value pairs  │
│           │          │ in the same order and of the same types.         │
└───────────┴──────────┴──────────────────────────────────────────────────┘


和以前一样，我们可以用一些测试代码简单地测试一下:

/**
/*
/* Testing operators: == and ===
/*
 */ 

//Test case
//Variations: amount, values and keys (order)
//Test count: 5
//    Failed: 0
//    Passed: 5     
{
    //Test case 2.1
    $a = [1];
    $b = [1];

    //Passed
    var_dump("Same amount of elements, values and keys: " . "'==' -> " . bool2str($a == $b) . " '===' -> " . bool2str($a === $b));
   
    //Test case 2.2
    $a = [1];
    $b = [10, 1];

    //Passed
    var_dump("NOT same amount of elements, but same values: " . "'==' -> " . bool2str($a == $b) . " '===' -> " . bool2str($a === $b));

    //Test case 2.3
    $a = [10];
    $b = [1];

    //Passed
    var_dump("Same amount of elements, but not values: " . "'==' -> " . bool2str($a == $b) . " '===' -> " . bool2str($a === $b));
    
    //Test case 2.4
    $a = [1 => 1];
    $b = [10 => 1];

    //Passed
    var_dump("Same amount of elements and values, but not keys: " . "'==' -> " . bool2str($a == $b) . " '===' -> " . bool2str($a === $b));
    
    //Test case 2.5
    $a = [1 => 1, 2 => 2];
    $b = [2 => 2, 1 => 1];

    //Passed
    var_dump("Same amount of elements, key and values, but different order: " . "'==' -> " . bool2str($a == $b) . " '===' -> " . bool2str($a === $b));
    
}


echo PHP_EOL . PHP_EOL . PHP_EOL;  //Test case separator

/**
/*
/* Test case end
/*
 */

//NULL, TRUE, FALSE 2 str func
function bool2str($v){if($v === NULL)return "NULL";elseif($v === FALSE)return "FALSE";elseif($v === TRUE)return "TRUE";else return "UNEXPECTED: '$v'";}


因此，我们可以看到并确认数组的比较运算符按预期和文档工作!

Full Testing File

对象比较运算符
< 的文档> 和对象被记录在案 here :

┌───────────┬───────────┬──────────────────────────────────────────────────┐
│ type of   │ type of   │                                                  │
│ Operand 1 │ Operand 2 │ Result                                           │
├───────────┼───────────┼──────────────────────────────────────────────────┤
│ object    │ object    │ Built-in classes can define its own comparison,  │  
│           │           │ different classes are uncomparable,              │
│           │           │ same class compare properties same as arrays     │
└───────────┴───────────┴──────────────────────────────────────────────────┘


和以前一样，我们也可以对此进行测试:

/**
/*
/* Testing operators: < and >
/*
 */ 

//Test case
//Variations: amount, values and keys (order)
//Test count: 10
//    Failed: 0
//    Passed: 10    
{
    //Test case 1.1
    $a = (object)["a" => 1];
    $b = (object)["a" => 1];

    //Passed
    var_dump("Same amount of elements, keys and values: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
   
    //Test case 1.2
    $a = (object)["a" => 1];
    $b = (object)["a" => 1, "b" => 1];

    //Passed
    var_dump("NOT same amount of elements, but same values: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));

    //Test case 1.3 
    $a = (object)["a" => 10];
    $b = (object)["a" => 1, "b" => 1];

    //Passed
    var_dump("NOT same amount of elements nor values: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
    
    //Test case 1.4
    $a = (object)["a" => 1];
    $b = (object)["b" => 1];

    //Passed
    var_dump("Same amount of element and values, NOT same keys: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));

    //Test case 1.5
    $a = (object)["a" => 10];
    $b = (object)["a" => 1];

    //Passed
    var_dump("Same amount of elements and keys, NOT same values: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
    
    //Test case 1.6
    $a = (object)["a" => 1, "b" => 1];
    $b = (object)["b" => 1, "a" => 1];

    //Passed
    var_dump("Same amount of elements and keys in different order: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
    
    //Test case 1.7
    $a = (object)["a" => 1, "b" => 5];
    $b = (object)["b" => 5];

    //Passed
    var_dump("Same values, NOT same amount of elements nor keys: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
    
    //Test case 1.8
    $a = (object)["c" => 1];
    $b = (object)["a" => 10];

    //Passed
    var_dump("NOT same keys nor values: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
    
    //Test case 1.9
    $a = (object)["a" => 1, "b" => 1];
    $b = (object)["b" => 10, "a" => 1];

    //Passed
    var_dump("Same amount of elements and values, NOT same keys nor order: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
    
    //Test case 1.10
    class A {public $a = 1;}
    $a = new A;
    class B {public $a = 1;}
    $b = new B;

    //Passed
    var_dump("Same amount of elements and values and keys, but different  not built-in class: " . "'<' -> " . bool2str($a < $b) . " '>' -> " . bool2str($a > $b));
    
}


echo PHP_EOL . PHP_EOL . PHP_EOL;  //Test case separator

/**
/*
/* Test case end
/*
 */

//NULL, TRUE, FALSE 2 str func
function bool2str($v){if($v === NULL)return "NULL";elseif($v === FALSE)return "FALSE";elseif($v === TRUE)return "TRUE";else return "UNEXPECTED: '$v'";}


带有对象的 == 和 === 的文档有自己的页面 here :

When using the comparison operator (==), object variables are compared in a simple manner, namely: Two object instances are equal if they have the same attributes and values, and are instances of the same class.

When using the identity operator (===), object variables are identical if and only if they refer to the same instance of the same class.



这可以再次测试:

/**
/*
/* Testing operators: == and ===
/*
 */ 

//Test case
//Variations: amount, values and keys (order)
//Test count: 7
//    Failed: 0
//    Passed: 7    
{
    //Test case 2.1
    $a = (object)["a" => 1];
    $b = (object)["a" => 1];

    //Passed
    var_dump("Same amount of elements, values and keys: " . "'==' -> " . bool2str($a == $b) . " '===' -> " . bool2str($a === $b));
   
    //Test case 2.2
    $a = (object)["a" => 1];
    $b = (object)["a" => 10, "b" => 1];

    //Passed
    var_dump("NOT same amount of elements, but same values: " . "'==' -> " . bool2str($a == $b) . " '===' -> " . bool2str($a === $b));

    //Test case 2.3
    $a = (object)["a" => 10];
    $b = (object)["a" => 1];

    //Passed
    var_dump("Same amount of elements, but not values: " . "'==' -> " . bool2str($a == $b) . " '===' -> " . bool2str($a === $b));
    
    //Test case 2.4
    $a = (object)["a" => 1];
    $b = (object)["b" => 1];

    //Passed
    var_dump("Same amount of elements and values, but not keys: " . "'==' -> " . bool2str($a == $b) . " '===' -> " . bool2str($a === $b));
    
    //Test case 2.5
    $a = (object)["a" => 1, "b" => 2];
    $b = (object)["b" => 2, "a" => 1];

    //Passed
    var_dump("Same amount of elements, key and values, but different order: " . "'==' -> " . bool2str($a == $b) . " '===' -> " . bool2str($a === $b));
    
    //Test case 2.6
    class C {public $a = 1;}
    $a = new A;
    class D {public $a = 1;}
    $b = new B;

    //Passed
    var_dump("Same amount of elements and values and keys, but different  not built-in class: " . "'==' -> " . bool2str($a == $b) . " '===' -> " . bool2str($a === $b));
    
    //Test case 2.7
    $a = (object)["a" => 1];
    $b = $a;

    //Passed
    var_dump("Same exact instance: " . "'==' -> " . bool2str($a == $b) . " '===' -> " . bool2str($a === $b));
    
}


echo PHP_EOL . PHP_EOL . PHP_EOL;  //Test case separator

/**
/*
/* Test case end
/*
 */

//NULL, TRUE, FALSE 2 str func
function bool2str($v){if($v === NULL)return "NULL";elseif($v === FALSE)return "FALSE";elseif($v === TRUE)return "TRUE";else return "UNEXPECTED: '$v'";}


所以我们看到，带有对象的比较运算符的行为与预期和记录的完全一样!即使进行松散的比较，也会考虑属性和值。

Full Testing File

结论

由于此错误已报告 here ，因此错误报告可能基于 RFC 中的评论，其中说:

// only values are compared



但除了这是 RFC 中唯一带有注释的示例之外，RFC 明确指出它使用与 < 、 == 和 > 相同的比较规则。

这意味着提供的代码示例将是无与伦比的，因为它没有相同的属性/键。

至于相等，它需要相同的属性/键和值，因此它不能相等，并且对于小于或大于它是不可比较的，如上面的代码示例所示，比较如何工作:
if (!array_key_exists($key, $op2)) {
    return null; // uncomparable
}

如果我们单独尝试每个比较运算符，我们也会看到这一点:
$a = (object)["b" => "b"]; 
$b = (object)["a" => "b"]; 


var_dump($a > $b);   //FALSE
var_dump($a < $b);   //FALSE
var_dump($a == $b);  //FALSE

都返回 false，因为它是无与伦比的。

对于 StdClass 有自己的比较的情况，我们可以用我们自己的类来测试它:

class A {
public $a = "";
public $b = "";
}

$a = new A;
$a->a = "b";
unset($a->b);

$b = new A;
$b->b = "b";
unset($b->a);

var_dump($a);
var_dump($b);

var_dump($a <=> $b); //1


同样的输出:1。

所以我会说，因为它是无与伦比的，所以它不应该返回 0 、 1 或 -1 。它可能应该返回 FALSE 或 NULL 或类似的东西。

现在我会说这种行为没有正确记录。

关于php - 运算符 <=> 如何比较对象？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/36246993/

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