src/Map.php
protected function walk(callable $code)
    {
        foreach ($this->array as $hash => &$value) {
            $key = $this->hash_to_key($hash);
            if (! $this->passes($this->call($code, $value, $key))) {
                break;
            }
        }
        return $this;
    }
protected function walk(callable $code)
    {
        foreach ($this->array as $hash => &$value) {
            $key = $this->hash_to_key($hash);
            if (! $this->passes($this->call($code, $value, $key))) {
                break;
            }
        }
        return $this;
    }
protected function walk ( callable $ code ) { foreach ( $ this -> array as $ hash => & $ value ) { $ key = $ this -> hash_to_key ( $ hash ) ; if ( ! $ this -> passes ( $ this -> call ( $ code , $ value , $ key ) ) ) { break ; } } return $ this ; }
Execute the given code over each element of the map. The code receives
the value by reference and then the key as formal parameters.

The items are walked in the order they exist in the map. If the code
returns boolean false, then the iteration halts. Values can be modified
from within the callback, but not keys.

Example:
```
$map->each(function (&$value, $key) { $value++; return true; })->sum();
```

@param callable $code
@return $this
Execute the given code over each element of the map . The code receives the value by reference and then the key as formal parameters .