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A sometimes useful concept inside of PHP is that of variable functions. This is a way for you to use a variable's value to call a function of the same name.
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A sometimes useful concept inside of PHP
is that of variable functions.
0:00
This is a way for you to use a variable's
value to call a function of the same name.
0:06
This way if a variable name has
parenthesis appended to it, PHP will look
0:11
for a function with the same name as
whatever the variable evaluates to,
0:16
and then will attempt to execute it.
0:20
We will use this mostly as a callback in
our code,
0:23
allowing us to call different functions
from another function or
0:25
from an action based off of the result of
the main function.
0:28
Let's go to Workspaces and look at this a
bit closer.
0:32
>> Okay.
So, let's open up some php tags here and
0:36
we have existing functions already for
hello and greet.
0:39
Well now, let's say function is equal to
hello.
0:43
So, this is just simple, variable named
func, F-U-N-C, or function.
0:47
And then, we set it equal to hello.
0:52
Now, this variable can be named anything,
just like a normal string variable.
0:54
You could name it, you know, Bob, Chris,
Tom, but it makes sense that
0:58
we're going to use a function name, so
we'll just say, func equals hello.
1:02
Now, in order to call it we simply use
$func, but then open and
1:08
close parentheses, and put a semi colon
after it.
1:12
This is the exact same as if we called
hello with open and
1:16
close parentheses, because in variable
functions inside of
1:19
php whatever the value of the variable
name is.
1:23
Which the value is hello of $func, it will
call that function, or
1:27
look for a function with that same name.
1:31
So, let's say we change $func to greet, and
then called F-U-N-C, or
1:35
$func with the open and close parentheses.
1:39
It would be the same as if we had called
greet.
1:42
We can also pass through arguments such as
dollar sign $func and then Mike and
1:45
then evening.
1:50
This would be the exact same as if we
called greet then Mike
1:51
then comma then evening.
1:55
Okay.
So, where we left off we actually have
1:58
a function here called add_up.
2:01
Let's say, we'll call it add_up and then
we'll have another one and
2:03
we'll call it subtract.
2:07
So, first thing we're gonna do is just
simplify these just to make them nice and
2:09
clean for now.
2:13
We'll actually return just $a plus $b.
2:15
Okay.
2:19
Save that, and then we want to add up
those two values, which is totally fine.
2:20
And then, we'll add another function in
here.
2:27
And, we'll call it, answer.
2:31
Okay?
And then,
2:36
that answer won't have any arguments, but
we will create it none the less.
2:37
And we'll say, return, and then we will
return the integer 42.
2:43
Okay.
2:47
So now, we have our return value of 42
from the answer function and
2:49
then we add up two values.
2:54
And then here, we have us calling add_up.
2:56
We're actually gonna remove this for right
now.
2:58
Okay.
So,
3:01
to talk about variable functions, we have
two functions here.
3:01
The idea behind a variable function is
that we're actually able to
3:05
call a function by using a string
variable.
3:10
So, let's try this by creating a new
variable, a string variable.
3:13
And, we'll call it func, F-U-N-C.
3:17
We'll set that equal to a string called
answer.
3:20
All right.
3:24
So, nothing more than just a string
variable.
3:26
But, in php, if we wanna call maybe a
function called answer,
3:29
we can do that by simply saying func,
which is our variable and
3:33
then adding a open and close parenthesis
around it, and then doing a semi colon.
3:38
So, I'm gonna save this and then go over
to our preview, and see what we get.
3:43
Okay.
We got nothing back.
3:49
The reason why, is we didn't actually echo
anything.
3:51
So, let's actually do echo of func.
3:53
Head back over after saving it and
refresh.
3:57
Perfect, 42.
We can actually store this to another
4:00
variable if you want.
4:03
So, we'll just call it num is equal to
func(); and then say, echo num.
4:04
Save it, go back over, and Refresh.
4:12
And, we get the same thing, 42.
4:15
We just went about it a different way.
4:16
All right.
4:18
So, that's a base of any kind of variable
function.
4:19
But, let's say we wanna change this easily
without modifying it at all.
4:24
We'll just say, change our string variable
value to add_up.
4:28
Now, this unto itself won't do us much
good.
4:33
We refresh it and we get 0.
4:36
Well, that's because adding 0 and 0 we get
0.
4:37
So, we can actually pass through arguments
right here on line 13.
4:41
So, we can say 5 and then 10.
4:45
Save that, head back over, and refresh.
4:49
And, we'll get 15.
4:53
So, what you can see here with variable
functions is that it
4:54
allows us to take input from somewhere
and
4:58
call any kind of function that preexists,
based off of a string variable value.
5:02
This could be very helpful for callbacks,
which we'll get into in later lessons.
5:08
But for now, you can see that just simply
taking a variable value, such as add_up or
5:12
answer, and putting parens behind that
function, or
5:17
behind that variable definition, you can
actually call a variable function.
5:21
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