Flutter 6 - Advanced Functions Video Lecture | Flutter: Build beautiful native apps in record time - App Development

everybody this is Brian and welcome to
the sixth tutorial on flutter we're
gonna continue down our path with dart
I'm gonna try and go through these
fairly quickly but because dart is a new
language and there's new features we got
to go through some of this elementary
stuff so so many more advanced folks
just bear with me while we slog through
this there are some new features so
definitely pay attention and I'll try to
call them out when I get there
so this is going to be our advanced
functions tutorial so the first thing
we're going to do is just create a new
project here make sure it's dart console
application and let's call this its funk
why now I'm really hard time coming up
with names for the sternness stuff and
it'll process and do its thing tick tock
tick tock intellij s' always so slow
there we go alright so we've covered
some of this stuff before we've got our
calculate function which is off in the
lib and we're gonna actually use that
this tutorial so if you're curious about
how that works definitely pay attention
all right so we're going to go ahead and
just get rid of this we're going to
leave this up here this time and we're
gonna cover that in just a second but
let's get through the rest of this first
so in our main function we want to make
a variable let's just say list my
keywords crooked bear with me here this
is what happens when you get old and
cranky so we're gonna make a list with
an integer type call it list and if you
remember these little brackets with the
type in it is generic programming
because that list can hold more than one
type and then in our list we're just
going to add a few values so we'll say 1
and I'm not going to really add too many
variables I'm actually just going to use
this one variable because you know this
is a function tutorial and I don't
really want to spend a lot of time
wasting your time writing variables so I
know a lot of tutorials out there have
like these big weird complex algorithms
that are hard to understand we're not
doing that all right so we've got our
variable that we're going to work with
so the first thing we're gonna cover is
a function as an object
maybe if I could spell object so what
does that really mean let's just make
our function here nothing super special
about this right and we're just going to
say print all right there's really
nothing going on in there
if you remember everything in dart is an
object and I mean everything it right
down to functions so we're gonna say
list for each now you notice how there's
a little bit of verbage here for each
and then there's parenthesis int and
then the arrow and then void
something-something we're just gonna
double click it from the moment and you
see how it says void F element eat
element sorry so really what that saying
is it cannot return anything void and
the function itself is going to take the
element now the element goes back to
generic programming under the hood this
actually says something like this list E
and E would be the representation of
whatever object were shoving in there so
the template for this thing has to be
void cannot return something and then it
has to take the element so we're just
going to say as object
finish this off with our semicolon here
and let's actually because we're gonna
make a bunch of these I just finished
watching stranger things last night oh
my god I show us so good but now I'm
trying to find other things to watch
like a Netflix junkie alright so when we
run this this is what happens it says as
an object BAM
and then lists for each and then we're
calling the actual function as an object
itself this object is instigated when
the code is run so we don't have to do
this you know neo blah blah blah it
already exists in memory and there's one
copy of it so as object and then that
has to follow the template so if we do
something like this it may get kind of
Frankie on us and say hey nope yep see
argument in string boy cannot be
assigned blah blah blah blah basically
what that's saying is it has to follow
the template and the template is you're
passing one element which is in that
list so that is a function as an object
I tend to not use that too much because
then the code gets kind of weird you're
trying to hunt down this thing and
figure out what's going on but if you
just want to go through it then you know
I guess it's okay what I tend to do is
yeah I'm just gonna copy and paste this
whole thing rather than type that all
out bang as an anonymous function I'm
lazy I really didn't want to spell
anonymous like six times this keyboards
kind of jackin with me I need a new one
that's playing call of duty and
admittedly I slammed my fist down on the
keyboard and now it's acting kind of
crazy so anyways so we're gonna do for
each now this time we're gonna do
something a little different we're gonna
do what's called an anonymous function
now an anonymous function has kind of a
crazy syntax but it'll save you a lot of
headache what you can do is say for each
and then we're going to just say
parenthesis I and then bracket
and don't forget to close this out with
a semicolon and we're just going to say
print hi this is bananas what is this
let's run this make sure this actually
works so as an anonymous function bang
what the heck is going on here so what
we're really doing is we're creating a
function in memory that only exists in
this little loop here it actually under
the hood gets optimized and it turns
into a temporary function in the base
code or whatever but for our purposes we
don't have to jump around all over the
place we just know that hey we want to
do this and we want to do it right here
so it does the exact same thing as this
it's just you don't have an independent
function that you can call as an object
notice the syntax is we have our
parameters and then we have our brackets
so we have our scope block here and then
we have our actual code of what we're
going to run pretty simple pretty
elegant I actually hated anonymous
functions when I first saw them but I
think I first saw them in Java and they
just drove me nuts but they're pretty
useful as you can see you don't have to
make it a separate function now if
you're going to call this many many
times
like over the course of your entire
program then definitely branch it off
into a first-class function right here
so now we're going to X jure see what I
mean about my keyboard turned all
external why can't you not spell
keyboard I'm going to best buying it
anyone forget this external function so
what is an external function we've been
talking about this little file over here
for a while now let's crack this back
open you see how it's got a function
that returns an integer
it's called calculate and it has no
parameters and then it just returns six
times seven we can actually call that
externally so let's just say print and
how do we know what to do I mean how do
we call that thing can we just say
calculate notice how when you start
typing calculate it recommends adv func
calc where'd it get that name from
let's just double-click it so it puts it
in there for us it actually got it up
here from this import statement that we
left and if you accidentally delete it
go ahead and retype all that in but it's
very simple import and then we're
importing a package semicolon and then
the path to that package adv func is
actually the name of our project here
ADB func and then the actual dart file
adv func dot dart down here as and this
is where we're creating the variable so
really it's that yeah we can run this
and you can see the results of that is
42 so let's crack this open let's just
add another one here let's say bull
loves my love's this keyboard string
name
so if you know the person in this
function is Brian B then I do not love
my keyboard otherwise we're going to
return true because everybody else in
the world loves their keyboard
especially when they're playing call of
duty little bastards all right so as you
can see whoops
loves this keyboard and then we could
say I'm so buying a new keyboard
and there's our false so how would you
actually you know go about making your
own here you can actually make a new one
we'll just call the start file let's
call this my file dot d 8 RT and rather
than typing that out again we're just
going to cut this put it in our little
file that was how way we did that
suddenly made that Dart got cranky
because this no longer exists so now we
got to make another import we're
importing a package and there's
different types of imports but we're
just gonna cover a package for today you
notice how it actually tries to help you
out so we're gonna import a DB funk
slash my file dart the file we just
created now we make we need to make it
as a variable and let's call this call
of duty
it is currently grayed out because it's
unused we're going to actually change
that bank now suddenly it's used does
the same thing so that is how you would
import an external function now the next
one's going to get a little bit crazy
but this is the last one in our little
tutorial here we're going to compare
apples to oranges you've heard that
expression before if you're in the
United States or maybe even if you're
out of the United States so we're going
to make optional parameters here and
we're going to say int apples equals 0
and int orange which is equals 0
and then we're just gonna simply say
compared to other number and actually we
don't have to do any that we can just
return it I had different in my little
notes here how I did it but actually
we'll there we go maybe there we go
mmm that didn't work either what did I
do wrong here
Richard type it oh that's why cuz it's
doing an N type man
so the compareto function is something I
really didn't want to use but basically
let's just switch this just so we can
see compared to used for ordering and
lists which we'll cover in a future
tutorial but let's just do this what
we're really focusing on is this part
right here we have our function and all
this does is it has optional parameters
notice these are optional but they're
optional because they're within these
brackets and they have a default value
and we're just going to say man
are you possessed keyboard what are you
doing here geez
alright so naming a naming a parameter
and we're going to just safe prints
compare notice how you can actually put
the parameter name in there
and then hit enter and it's giving us a
negative one because they're not so
let's just change this to nine and
that's a three you see how it's now a
one because it does an ordering thing I
was going to use a pool but let's just
say this is six and this is six and it
should come back as zero meaning they
are equal so why would you want to
actually name your parameter why can't
you just you know do the order here very
simple a lot of more advanced code will
actually use name parameters when you
get in a flutter you'll actually use
them quite a bit and it's just an
elegant way of saying hey this is
actually going to be this and I just
want to test this I want to actually
move this around so you notice how we've
actually got it backwards in the compare
statement it's apples then oranges but
we're actually seeing oranges than
apples this would normally throw an
error in other languages a book should
run just fine and it does so that is
also why you would use it if you don't
want to use an ordered list or an
ordered list of parameters so more
information go out and read the official
documentation in optional parameters and
you can see how when calling a function
you can specify name parameters etc etc
definitely read up their documentation
it's well worth the read I know it's a
little bit lengthy but I can't possibly
cover everything in these videos if you
found this educational entertaining the
source code will be out on the website
you can just click for the link out
github and there is a boy drums Facebook
group with I think seventeen hundred
other programmers out there all walks of
life we can definitely help you out with
any issues you come up with
unfortunately I get just an extreme
amount of email I've actually had to
make a separate account and hide it from
the world just as I couldn't do anything
with it so don't email me go out to the
void Rome's Facebook group and go out to
get hub get the code I'll talk to you
guys later thanks