基本参数问题

Question

I just started learning PHP and I have some questions about the parameters. Consider DateTime class PHP DateTime Class Manual

public __construct ([ string $time = "now" [, DateTimeZone $timezone = NULL ]] )
public DateTime setDate ( int $year , int $month , int $day )

Here's my question:

1. Why the parameters in the constructor are in brackets when setDate parameters aren't in brackets?
2. Why there's bracket within a bracket?
3. Why there's comma before the open bracket, [, ?

Thanks in advance.

Answer 1

1. The parameters in brackets are optional. Therefore, if I initialize the DateTime class and don't provide the second parameter, it takes the default value of null.

2. Nested brackets just means this: If I were to initialize the DateTime class, I provid either parameter 1 or parameter 1 and 2, or none at all. I cannot opt to provide no parameter 1, but a value for parameter 2.

3. The comma just seperates the different parameters in the function's signature if more than 1 is provided..