What will be the result of each of the following lines of code

Consider the following two methods:

def times_two(arg1);
   puts arg1 * 2;
end
    
def sum(arg1, arg2);
   puts arg1 + arg2;
end

What will be the result of each of the following lines of code:

times_two 5
times_two(5)
times_two (5)
sum 1, 2
sum(1, 2)
sum (1, 2)

The first three lines of code will all print out 10, as expected. The next two lines of code will both print out 3, as expected.

However, the last line of code (i.e., sum (1,2)) will result in the following:

    syntax error, unexpected ',', expecting ')'
    sum (1, 2)
           ^

The problem is the space between the method name and the open parenthesis. Because of the space, the Ruby parser thinks that (1, 2) is an expression that represents a single argument, but (1, 2) is not a valid Ruby expression, hence the error.

Note that the problem does not occur with single argument methods (as shown with our timesTwo method above), since the single value is a valid expression (e.g., (5) is a valid expression which simply evaluates to 5).