How to use class variable as default value in php functions?

You can not do this, the default parameter values must be constant. The maximum that PHP allows is to use class constants, with static reference:

class Teste {
  const VARIAVEL = 10;
  const VARIAVELA = 20;

  function __construct($parametro=self::VARIAVEL, $parametro2=self::VARIAVELA){
    echo "$parametro - $parametro2";
  }
}

$t = new Teste();

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Although in this case it's worth putting the literal values directly into the function signature, is not it? It gets cleaner:

class Teste {   
  function __construct($parametro=10, $parametro2=20){
    echo "$parametro - $parametro2";
  }
}

$t = new Teste();

If you need a solution with dynamic values, assign the values within the function itself, as @ AndréRibeiro suggested in his response .

What you are trying to do is not valid in PHP.

According to the manual :

  

The default [of a function parameter] must be a constant expression, not (for example)   a variable, a class member, or a function call.

An alternative with similar functionality:

class Teste(){
  public $variavel;
  public $variavela;

  function teste($parametro = null, $parametro2 = null){
    $parametro = $parametro ? $parametro : $this->variavel;
    $parametro2 = $parametro2 ? $parametro2 : $this->variavela
  }
}

In this example, if any of the parameters are not passed in the function call, the default value is the value of the class member.