What is the purpose of {} in the code below? and what is the definition?

Official Documentation

It basically serves to define the beginning and the end of the method name that should be invoked. As the name varies by the value of $tipo , just do:

$objeto->'getEndereco' . ucfirst($tipo)()->getCep();

It will generate a syntax error, because PHP will not know what to do with a constant after the -> operator.

  

Syntax error, unexpected '' getEndereco '' (T_CONSTANT_ENCAPSED_STRING), expecting identifier (T_STRING) or variable (T_VARIABLE) or '{' or '$'

Notice that the error itself says that a T_STRING would be expected, which in this case will be only getEndereco , without quotation marks, or a variable or the { character. That is, the {} characters indicate to PHP to interpret the internal value as the method name and not as any constant.

Run the displayed code:

$objeto->{'getEndereco' . ucfirst($tipo)}()->getCep();

It's analogous to doing:

$endereco = call_user_func([$objeto, 'getEndereco' . ucfirst($tipo)]);
$endereco->getCep();

However, in certain situations it is more convenient to only chain calls using {} . It is also possible to chain this notation. For example:

$foo = "Hello";
$bar = "foo";

echo "${${'bar'}} world"; // Hello world

Because% of% is interpreted as {'bar'} , then% of% is treated as the variable bar , whose value is ${'bar'} . Then, $bar will be interpreted as "foo" and {${'bar'}} will be treated as the foo variable, displaying its content, ${${'bar'}} .

In PHP 7+ versions you can also use $foo together with "Hello" to import multiple classes from the same namespace :

use Meu\Namespace\{ClasseA, ClasseB, ClasseC};

Previous versions would require:

use Meu\Namespace\ClasseA;
use Meu\Namespace\ClasseB;
use Meu\Namespace\ClasseC;

This is to access the object dynamically. Let's assume that $ type has the following content:

$tipo = 'Residencial';

// Forma correta dinâmica
$objeto->{'getEndereco' . ucfirst($tipo)}()->getCep();

// Forma correta direta
$objeto->getEnderecoResidencial()->getCep();

// Todas as duas opções acima irão acessar a função do objeto e obter o getCep:
$objeto->getEnderecoResidencial()->getCep;

// Formas INcorretas
$objeto->'getEndereco' . ucfirst($tipo)()->getCep();
$objeto['getEndereco' . ucfirst($tipo)]()->getCep();
$objeto['getEnderecoResidencial']()->getCep();

In PHP there are N ways to write a string , one of them is called Sintaxe complexa .

The name is not really due to the complexity of the syntax, but rather because of the complex expressions that can be written this way.

According to the documentation itself:

  

Any scalar variable, element of an array or property of a   object with a representation of a string can be included with this   syntax. Simply write the expression the same as   would appear outside of the string and then put it between {e}. Since that {   can not be escaped, this syntax will only be recognized when $   immediately follow the {. Use {\ $ to get a literal {$.