PHP warning Illegal offset type error solution

In a word, the object is used as the key of the array. For example, the following code triggers this warning:

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$ Arr = array ();    Class    {    }    $ O = new;    Echo $ arr [$ o];

Specifically, I triggered this warning when I was working on a Yii multi-language site. I wrote:

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Yii: app ()-> language = Yii: app ()-> request-> cookies ['Lang '];

The following error is reported:

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$ This-> _ files [$ category] [$ language] = $ this-> basePath. DIRECTORY_SEPARATOR. $ language. DIRECTORY_SEPARATOR. $ category. '. Php '; 124} Yii: app ()-> language = Yii: app ()-> request-> cookies ['Lang ']-> value;

The code is as follows: