<?php
/**
 * Created by PhpStorm.
 * User: hongxu
 * Date: 16/8/4
 * Time: 13:21
 */

class str {

    private $str = '';

    /**
     * str constructor.
     */
    public function __construct($str) {

        $this->str = $str;
    }

    public function trim() {
        $this->str = trim($this->str);
        return $this;
    }

    public function strlen() {
        return strlen($this->str);
    }
}

$str = new str('要思考,不做伸手党');

var_dump($str->trim()->strlen());die;

output:

php test.php
int(25)

<?php
class Str {
    private $value = '';

    public function __construct($str) {
        $this->value = $str;
    }

    public function __call($name, $args) {
        if (function_exists($name)) {
            array_unshift($args, $this->value);
            $value = call_user_func_array($name, $args);
            if (is_string($value)) {
                return new static($value);
            } else {
                return $value;
            }
        }
    }

    public function __toString() {
        return $this->value;
    }
}

$str = new Str('  题主是不是个伸手党?  ');

echo($str->trim() . PHP_EOL);
echo($str->trim()->strlen() . PHP_EOL);
$trim_str = $str->trim();
echo($trim_str->substr(0, $trim_str->strlen() - 1) . PHP_EOL);

题主是不是个伸手党?
28
题主是不是个伸手党

要实现这样的功能并不难，只需要对string进行封装一下。如果需要链式调用，则可台返回$this即可。
请看如下代码，即可实现您的功能：

<?php
//演示链式调用

class MyString{
    private $string;
    
    function MyString($str){
        $this->string=$str;
    }
    
    function len(){
        return strlen($this->string);
    }
    
    function _trim(){
        $this->string=trim($this->string);
        return $this;
    }
}

$d=new MyString(' sdfsdf  ');
echo $d->_trim()->len();
?>

->为什么要空格 = =，看上去好奇怪