对象运算符中的变量 [英] Variables within object operators

问题描述

我正在尝试在PHP中设置基于变量的对象运算符，但只能在有限的范围内完成我要寻找的内容.例如，以下代码允许选择变量:

I’m attempting to set up a variable-based object operator in PHP, but am only able to accomplish what I am looking for to a limited extent. For example, the following code allows for variable selection:

$var1 = 'available_from';
$keyValuePairs[$key] = $item->parent()->{$var1};

但是，如果我也想使父选择器成为变量，我似乎不再能够.以下两种方法均会失败:

However, if I want to make the parent selector a variable as well, I no longer seem to be able to. Both of the following methods fail:

$var1 = 'parent()->available_from';
$keyValuePairs[$key] = $item->{$var1};

和

$var1 = 'parent()';
$var2 = 'available_from';
$keyValuePairs[$key] = $item->{$var1}->{$var2};

所以问题是是否有办法做到这一点.

So the question is whether there is a way to do this.

推荐答案

您基本上可以做到这一点，但必须将括号放在外面.

You can basically do that, but you have to put the parens on the outside.

$var1 = 'parent';
$var2 = 'available_from';
$keyValuePairs[$key] = $item->{$var1}()->{$var2};
// or $keyValuePairs[$key] = $item->$var1()->{$var2};

如果不使用eval，基本上是没有办法解决的:

And there basically is no way of getting around that without using eval:

// escape the first $
$keyValuePairs[$key] = eval( "\$item->$var1->$var2" );

但是，如果您首先可以访问潜在的变量集，那么实际上没有理由使用eval.

But, there is really no reason to use eval if you have access to the potential set of variables first.

您可以执行以下操作来解决此问题:

You can do something like this to get around it:

function call_or_return( $obj, $prop )
{
    // test to see if it is a method (you'll need to remove the parens first)
    $arr = array( $obj, $prop );
    // if so call it.
    if( is_callable( $arr ) ) return call_user_func( $arr );
    // otherwise return it as a property
    return $obj->$prop;
}

call_or_return( $item, $var1 )->{$var2};

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