如何将一个函数的结果作为另一个函数的默认值传递？

Question

I have a function that is called without the user giving notice, and it just creates a row on my Database.
The function is this one:

public function createRow($year = 2015) {
    $query = DB::table('myTable')->where('year', '=', $year)->get()->first();
    // The rest of the function doesn't matter
}

The problem here is that I need the default value for this function to be the year before the actual year. In order to do that I tried to put this:

public function createRow($year = date('Y') - 1) {
    $query = DB::table('myTable')->where('year', '=', $year)->get()->first();
    // whatever
}

It's obvious it didn't work, so I did a really small function that return the year before the actual year, and I tried to use the result of the small function as the default parameter of the createRow() function:

public function lastYear() {
   return date('Y') - 1;
}
public function createRow($year = $this->lastYear()) {
    $query = DB::table('myTable')->where('year', '=', $year)->get()->first();
    // Whatever
}

I also tried defining a global variable:

protected $lastYear = date('Y') - 1;

but I got the error:

expression is not allowed as field default value

I hope you can help me with this.

Thank you very much.

Answer 1

Try this:

public function createRow($year = null) {
    if ($year == null)
    {
        $year = date('Y') - 1;
    }
    $query = DB::table('myTable')->where('year', '=', $year)->get()->first();
    // whatever
}

Answer 2

Try this

public function createRow($year) {

    if (!$year)
    {
        $year = date('Y') - 1;
    }

    $query = DB::table('myTable')->where('year', '=', $year)->get()->first();
    // whatever
}

You can change the if condition so if $year does not contain a valid value you can set the it the default value in the beginning of the function.