What’s the difference from . to -> in PHP?

Question

What is the difference between them? I took an exercise of "Aggregation Relationship" that had the 2, and did not understand the use of . instead of the ->

In this case, what is the difference, for example, of this:

$varTeste.abrirFuncao(); 

and from that:

$varTeste->abrirFuncao();

function lutar($l1, $l2){
        if($l1.getCategoria() == $l2.getCategoria()
                && ($l1 != $l2)){
                $this->aprovada = true;
                $this->desafiado = $l1;
                $this->desafiante = $l2;
        } else {

        }
    }

Source of the financial year: https://youtu.be/lOOYBUQSRWU?t=8m1s

Answer 1

The point (.) in the PHP is used to perform concatetion of strings as in the example below:

$nome = 'Meu nome';
$sobreNome = 'Meu sobrenome';
echo $nome.$sobreNome
// Saida: Meu NomeMeu sobrenome
// Note que não existem espaços entre os nome pois não são usados espaços nas strings.

The arrow (->) is used to call class functions, while other languages use ponto to call function the PHP uses these "little arrows", see the example:

// Java, Ruby, Javascript e etc...
classe.funcao();

// PHP
classe->funcao();

Answer 2

It was a typo. Run the video more and you will see that when it runs the program, the error appears.

https://youtu.be/lOOYBUQSRWU?t=15m26s

To access a method in PHP is only through the operator ->, or through the :: for static methods. The operator . concatenation, then execute the code:

$l1.getCategoria() == $l2.getCategoria()

PHP will try to concatenate the variable $l1 with the return of the function getCategoria() and try to concatenate the variable $l2 also with the return of the function getCategoria(), checking whether the final values are equal.

Take great care that this can generate a false positive. For example, let’s consider two objects in the class Foo:

$l1 = new Foo("lutador 1");
$l2 = new Foo("lutador 2");

var_dump($l1.getCategoria() == $l2.getCategoria());

Let’s assume that function getCategoria is defined in the program:

function getCategoria() {
    return "categoria";
}

If the class Foo have, for example, the method __toString:

class Foo {

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

    public function __toString() {
        return "classe Foo";
    }

}

When executing the code:

var_dump($l1.getCategoria() == $l2.getCategoria());

The exit will be bool(true), for the comparison will be "classe Foocategoria" == "classe Foocategoria". That is, instead of giving an error, your condition returned true in a if. This can generate unexpected results in the application and it will be very difficult to find the source of the error, because being a valid syntax, any interpreter will accept the code and will not show you even a warning.

See working on Ideone.

Imagine if you make the condition below:

if ($l1.getCategoria() == $l2.getCategoria()) {
    mysqli_query($conn, "DROP DATABASE sopt");
}

The damage it would cause because of a wrong operator...