Error PHP POO polymorphism

How we model our classes will depend on the behavior (rules) defined for the application. In the model below I considered that in your application, a person cannot be simply a person (Direct instance of the class), for this reason the constructor of the Class person has been set to protected, that is, it must be called by another class that inherits from person.

If we consider that Name, age and Gender are attributes primary of the class, we can use a constructor and receive this data already at the time we create an instance of the object. To retrieve the values I like to use the getAtributo approach, so I know that this public method is used to retrieve an attribute. The visual processing / formatting can be done by an auxiliary class or can be done directly in the file that calls the method.

See code:

<?php

class Pessoa{     

    private $nome;
    private $idade;
    private $sexo;  

    protected function __construct($nome, $idade, $sexo)
    {
        $this->nome = $nome;
        $this->idade = $idade;
        $this->sexo = $sexo;
    }

    protected function getNome()
    {
        return $this->nome;
    }

    protected function getIdade()
    {
        return $this->idade;
    }

    protected function getSexo()
    {
        return $this->sexo;
    }
} 

class Funcionario extends Pessoa
{ 
    private $empresa;
    private $salario;

    public function __construct($nome, $idade, $sexo, $empresa, $salario)
    {
        parent::__construct($nome, $idade, $sexo);
        $this->empresa = $empresa;
        $this->salario = $salario;
    }

    public function getEmpresa()
    {
        return $this->empresa;
    }

    public function getSalario()
    {
        return $this->salario;
    }
}

$funcionario = new Funcionario("Yuri", "19", "Masculino", "Tam", "3000");

echo $funcionario->getNome() . ' Trabalha na: ' . $funcionario->getEmpresa() . ' e ganha ' . $funcionario->getSalario();

Let's take a second approach. Personally I like to use the famous setAtributo to define the value of my variables, but why do I do this? Simple, to include validation in the assignment of values. The example below is quite simple and does not reflect an actual flow of data validation, but serves to pass an idea of how the thing works:

<?php

class Pessoa{     

    private $nome;
    private $idade;
    private $sexo;  

    protected function setNome($nome)
    {
        if(is_string($nome)) {
            $this->nome = $nome;
            return true;
        }

        return false;
    }

    protected function setIdade($idade)
    {
        if(is_int($idade)) {
            $this->idade = $idade;
            return true;
        }

        return false;
    }

    protected function setSexo($sexo)
    {
        if($sexo == 'M' || $sexo = "F") {
            $this->sexo = $sexo;
            return true;
        }

        return false;
    }

    public function getNome()
    {
        return $this->nome;
    }

    public function getIdade()
    {
        return $this->idade;
    }

    public function getSexo()
    {
        return $this->sexo;
    }
} 

class Funcionario extends Pessoa
{ 
    private $empresa;
    private $salario;

    public function __construct($nome, $idade, $sexo, $empresa, $salario)
    {
        self::setNome($nome);
        self::setIdade($idade);
        self::setSexo($sexo);
        $this->empresa = $empresa;
        $this->salario = $salario;
    }

    public function getEmpresa()
    {
        return $this->empresa;
    }

    public function getSalario()
    {
        return $this->salario;
    }
}

$funcionario = new Funcionario("Yuri", "19", "Masculino", "Tam", "3000");

echo $funcionario->getNome() . ' Trabalha na: ' . $funcionario->getEmpresa() . ' e ganha ' . $funcionario->getSalario();

Note: note that I used self::setNome in the Class Funcionario , however, it would also work as $this->setNome since we are talking about a inheritance, however, I prefer to use self as this makes it clear that the method was inherited and assigns semantics to the code.

You can still set the strick_types=1 and then work with input and output 'manual typing' (return). Here's a simple example:

<?php
declare(strict_types=1);

class Pessoa{     

    private $nome;
    private $idade;
    private $sexo;  

    protected function setNome(string $nome) : bool
    {
        if(!is_null($nome)) {
            $this->nome = $nome;
            return true;
        }

        return false;
    }

    protected function setIdade(int $idade) : bool
    {
        if(!is_null($idade)) {
            $this->idade = $idade;
            return true;
        }

        return false;
    }
    //...