Curly Braces Notation in PHP

问题

I was reading source of OpenCart and I ran into such expression below. Could someone explain it to me:

$quote = $this->{'model_shipping_' . $result['code']}->getQuote($shipping_address);

In the statement, there is a weird code part that is
$this->{'model_shipping_' . $result['code']}
which has {} and I wonder what that is? It looks an object to me but I am not really sure.

回答1:

Curly braces are used to denote string or variable interpolation in PHP. It allows you to create 'variable functions', which can allow you to call a function without explicitly knowing what it actually is.

Using this, you can create a property on an object almost like you would an array:

$property_name = 'foo';
$object->{$property_name} = 'bar';
// same as $object->foo = 'bar';

Or you can call one of a set of methods, if you have some sort of REST API class:

$allowed_methods = ('get', 'post', 'put', 'delete');
$method = strtolower($_SERVER['REQUEST_METHOD']); // eg, 'POST'

if (in_array($method, $allowed_methods)) {
    return $this->{$method}();
    // return $this->post();
}

It's also used in strings to more easily identify interpolation, if you want to:

$hello = 'Hello';
$result = "{$hello} world";

Of course these are simplifications. The purpose of your example code is to run one of a number of functions depending on the value of $result['code'].

回答2:

The name of the property is computed during runtime from two strings

Say, $result['code'] is 'abc', the accessed property will be

$this->model_shipping_abc

This is also helpful, if you have weird characters in your property or method names.

Otherwise there would be no way to distinguish between the following:

class A {
  public $f = 'f';
  public $func = 'uiae';
}

$a = new A();
echo $a->f . 'unc'; // "func"
echo $a->{'f' . 'unc'}; // "uiae"

回答3:

Curly braces are used to explicitly specify the end of a variable name.

https://stackoverflow.com/a/1147942/680578

http://php.net/manual/en/language.types.string.php#language.types.string.parsing.complex

来源：https://stackoverflow.com/questions/9056021/curly-braces-notation-in-php

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