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It's possible to return multiple
values from a single function.

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This is usually used
to communicate errors.

3
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You set this up by declaring multiple
return values within parentheses,

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following the parentheses that
accept parameters for the function.

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So here, we specify that this squareRoot
function is going to return one value

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that's a float64 type, and
then a second value that's an error type.

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Now, as you might be aware,

8
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it's not possible to take a square
root of a negative number.

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So, we've set our square root
function up to check for this.

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It looks at the parameter
that got passed in, x, and

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if it's less than 0 then we return
the value 0, which we're going to ignore.

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As well as the new error value, which we
get by calling the format packages Errorf

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function, and passing it a string, can't
take the square root of a negative number.

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If x is greater than 0, or equal to 0,
then we'll proceed as normal.

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We call the math packages
square root function and

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pass it the parameter that we got.

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We then return the value nil,
which represents that we have no error.

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We then handle those multiple return
values up here in the main function.

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We call square root, up here, and

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then we assign two variables at
once based on its return value.

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The square root variable will hopefully
contain the square root of whatever

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argument we pass the square root.

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And the error value will hopefully be nil.

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But in the event that there was a problem,
say if we were to call square

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root with a negative number,
the error value will not be nil.

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We'll have passed the return
value of this error f function,

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which will be an error value,
which will then logout to the console.

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Calling the fatal function
from the log packages cause

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your program to print an error message and
then exit immediately.

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So this line down here would never
be reached if there was an error.

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So, we handled the error here and

32
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in the event that there's not an error
we proceed to print out the square root.

33
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So let's try running this.

34
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Okay, and because we called square
root with a negative number we see

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our error message printed out here, can't
take square root of a negative number.

36
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Where as if we were to change this to a
valid value say get the square root of 9,

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if we try running this again
it runs successfully and

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it prints out our square root, 3.

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These function calls also
return multiple values.

40
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But in this case we're getting a compile
error because we aren't doing anything

41
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with the second value We're getting the
multiple value os.Stat() in single value

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context.

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We can get this code to compile
by adding the blank identifier.

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This will assign the second value,
the error value,

45
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from os.Stat to a throwaway variable,
this underscore that you see here.

46
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So if we have this down here as well
our program will then compile and run.

47
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So as you can see up
here that we get a file

48
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size for the existent text file.

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However down here we get a run time panic,
this is a special type of

50
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error that occurs after your program
compiles and while it's running.

51
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And that's something that you
want to avoid wherever possible.

52
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And this is why that assigning error
values to the blank identifier isn't

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always a good idea.

54
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In this case, checking the size
of the existent.txt file worked

55
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because that file was on the disk,
but, nonexistent.txt wasn't.

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And therefore we got an error which
we ignored and when we tried to print

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out the size on this invalid file
info object, our program panicked.

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We can fix this by checking to see if
the error return value from os.stat

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is anything other than nil.

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And if it is, handling the error.

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So instead of the blank identifier here,

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let's assign this error return
value to a variable called error.

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And here let's do a test.

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Let's say if the error
Is not equal to nil.

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Then we will print out the error.

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And if the error is nil, it means that
we got our file info back successfully.

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So we can move this format
print line file info.

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Size line up into the else clause.

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And we'll be able to print
the file info out successfully.

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We'll do the same down here following
getting os.stat for the second file.

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We need to be sure to assign
not to the blank Identifier,

72
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but to the error variable.

73
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We'll test if it's nil.

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If it's not nil,
we'll print out the error.

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Otherwise, we'll print out the file info.

76
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Now let's try running this again.

77
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And you see for
our first file we got a file size of 0,

78
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which, because it does exist but
its size is 0.

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And for
the second file it prints out our error.

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It tried to run stats on nonexistant.txt,
but there was no such file.