报告 bug 或提出建议。
DocumentationhackLearnExpressions And OperatorsEcho

Expressions And Operators: Echo

This intrinsic function converts the value of an expression to string (if necessary) and writes the string to standard output. For example:

$v1 = true;
$v2 = 123.45;
echo '>>'.$v1.'|'.$v2."<<\n"; // outputs ">>1|123<<"

$v3 = "abc{$v2}xyz";
echo "$v3\n";
Output 
>>1|123.45<<
abc123.45xyz

For a discussion of value substitution in strings, see string literals. For conversion to strings, see type conversion.

echo cannot output an array. However, echo can output the value of an object provided its type defines a __toString method. For example:

class Point {
  private float $x;
  private float $y;

  public function __construct(num $x = 0, num $y = 0) {
    $this->x = (float)$x;
    $this->y = (float)$y;
  }

  public function __toString(): string {
    return '('.$this->x.','.$this->y.')';
  }
  // ...
}

<<__EntryPoint>>
function main(): void {
  $p1 = new Point(20.5, 30.33);
  /* HH_FIXME[4067] implicit __toString() is now deprecated */
  echo $p1."\n"; // implicit call to __toString()
}
Output 
(20.5,30.33)