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A sometimes useful concept inside of PHP
is that of variable functions.

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This is a way for you to use a variable's
value to call a function of the same name.

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This way if a variable name has
parenthesis appended to it, PHP will look

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for a function with the same name as
whatever the variable evaluates to,

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and then will attempt to execute it.

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We will use this mostly as a callback in
our code,

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allowing us to call different functions
from another function or

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from an action based off of the result of
the main function.

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Let's go to Workspaces and look at this a
bit closer.

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>> Okay.
So, let's open up some php tags here and

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we have existing functions already for
hello and greet.

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Well now, let's say function is equal to
hello.

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So, this is just simple, variable named
func, F-U-N-C, or function.

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And then, we set it equal to hello.

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Now, this variable can be named anything,
just like a normal string variable.

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You could name it, you know, Bob, Chris,
Tom, but it makes sense that

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we're going to use a function name, so
we'll just say, func equals hello.

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Now, in order to call it we simply use
$func, but then open and

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close parentheses, and put a semi colon
after it.

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This is the exact same as if we called
hello with open and

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close parentheses, because in variable
functions inside of

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php whatever the value of the variable
name is.

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Which the value is hello of func, it will
call that function, or

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look for a function with that same name.

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So, let's say we change func to greet, and
then called F-U-N-C, or

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func with the open and close parentheses.

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It would be the same as if we had called
greet.

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We can also pass through arguments such as
dollar sign func and then Mike and

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then evening.

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This would be the exact same as if we
called greet then Mike

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then comma then evening.

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Okay.
So, where we left off we actually have

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a function here called add up.

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Let's say, we'll call it add up and then
we'll have another one and

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we'll call it subtract.

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So, first thing we're gonna do is just
simplify these just to make them nice and

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clean for now.

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We'll actually return just $a plus $b.

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Okay.

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Save that, and then we want to add up
those two values, which is totally fine.

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And then, we'll add another function in
here.

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And, we'll call it, answer.

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Okay?
And then,

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that answer won't have any arguments, but
we will create it none the less.

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And we'll say, return, and then we will
return the integer 42.

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Okay.

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So now, we have our return value of 42
from the answer function and

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then we add up two values.

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And then here, we have us calling add_up.

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We're actually gonna remove this for right
now.

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Okay.
So,

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to talk about variable functions, we have
two functions here.

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The idea behind a variable function is
that we're actually able to

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call a function by using a string
variable.

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So, let's try this by creating a new
variable, a string variable.

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And, we'll call it func, F-U-N-C.

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We'll set that equal to a string called
answer.

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All right.

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So, nothing more than just a string
variable.

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But, in php, if we wanna call maybe a
function called answer,

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we can do that by simply saying func,
which is our variable and

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then adding a open and close parenthesis
around it, and then doing a semi colon.

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So, I'm gonna save this and then go over
to our preview, and see what we get.

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Okay.
We got nothing back.

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The reason why, is we didn't actually echo
anything.

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So, let's actually do echo of func.

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Head back over after saving it and
refresh.

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Perfect, 42.
We can actually store this to another

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variable if you want.

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So, we'll just call it num is equal to
funk and then say, echo num.

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Save it, go back over, and Refresh.

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And, we get the same thing, 42.

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We just went about it a different way.

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All right.

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So, that's a base of any kind of variable
function.

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But, let's say we wanna change this easily
without modifying it at all.

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We'll just say, change our string variable
value to add up.

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Now, this unto itself won't do us much
good.

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We refresh it and we get 0.

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Well, that's because adding 0 and 0 we get
0.

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So, we can actually pass through arguments
right here on line 13.

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So, we can say 5 and then 10.

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Save that, head back over, and refresh.

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And, we'll get 15.

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So, what you can see here with variable
functions is that it

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as allows us to take input from somewhere
and

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call any kind of function that preexists,
based off of a string variable value.

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This could be very helpful for callbacks,
which we'll get into in later lessons.

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But for now, you can see that just simply
taking a variable value, such as add up or

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answer, and putting parents behind that
function, or

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behind that variable definition, you can
actually call a variable function.