No parenthesis might cause unexpected behavior.

dtest_1.d

import std.stdio;
 
void main()
{
    //Causes function number(int) to be called
    number = 4;
    
    //Declare integer number (same name as function)
    int number;
    //Set integer number to four. This will not call function number(int)
    number = 4;
}
 
void number(int n){
    writeln("printed once, ey?");
}

Outputs: printed once, ey?