WEBVTT 00:00.060 --> 00:04.740 Hello again! In this video, we are going to look at tuples in C++17. 00:06.480 --> 00:09.610 The first two features are ones that we have seen before, 00:09.630 --> 00:10.170 in fact. 00:11.600 --> 00:13.970 Constructor template argument deduction. 00:14.420 --> 00:20.030 If we have a constructor which is templated, we no longer need to provide the type parameters. 00:20.540 --> 00:24.170 If we have an initializer, then the compiler will work them out for us. 00:25.280 --> 00:31.430 So, for example, we can just create a tuple, from an initializer, and the compiler will deduce that 00:31.430 --> 00:34.070 the types of the elements are int, double and string. 00:34.490 --> 00:37.460 We no longer have to write them out explicitly. 00:39.930 --> 00:40.800 Structured bindings. 00:40.800 --> 00:43.860 We have used these to unpack the members of a pair. 00:44.370 --> 00:50.640 When we were working with map elements, for example. And we can also use structured bindings with tuples. 00:51.930 --> 00:57.720 If we have some function which returns a tuple, then we can just use the structured binding directly 00:58.200 --> 01:03.510 and this will create and initialize these variables, from the elements of the tuple. 01:03.900 --> 01:08.940 We no longer need to declare the variables and call the tie() function. 01:11.320 --> 01:12.360 So let's try this out. 01:12.400 --> 01:15.880 We have our tuple initialization here. 01:16.720 --> 01:18.760 We do not need to do that anymore. 01:19.240 --> 01:25.840 We return this tuple from the function. And then, in the caller, we use a structured binding to unpack 01:25.840 --> 01:28.330 the elements of the tuple, and we print them out. 01:30.580 --> 01:31.150 And there we are. 01:36.190 --> 01:40.030 One of the new functions in C++ is called apply(). 01:40.390 --> 01:43.750 This is for using a more functional style of programming. 01:44.830 --> 01:51.730 It takes a callable object as its first argument, and then it will call this function and pass the 01:51.730 --> 01:54.610 rest of the arguments, as arguments to this function. 01:55.270 --> 02:01.060 So if we have some function pointer as the first argument, then this will call the function pointer, 02:01.780 --> 02:03.910 and the rest of the arguments will be forwarded 02:04.030 --> 02:05.710 as arguments to that function call. 02:06.880 --> 02:11.260 Obviously, having to manage several different argument objects could be a bit annoying. 02:11.620 --> 02:17.590 So you can also use a tuple. So you can pack all these objects up into a tuple. And then, when you call 02:17.590 --> 02:23.650 apply(), apply() will unpack the tuple and forward the elements to the function call. 02:26.200 --> 02:28.060 So here is a very simple example. 02:28.420 --> 02:33.670 We have a function which prints out its arguments. And then we have this as the first argument to 02:33.670 --> 02:34.090 apply(). 02:34.120 --> 02:36.370 So that is a function pointer to this function. 02:37.180 --> 02:43.360 And then we have a tuple. And this will call the function, with those tuple elements as the arguments 02:43.360 --> 02:44.410 to the function call. 02:47.020 --> 02:47.650 And there we are. 02:49.270 --> 02:54.760 And finally, it is also possible to pass a tuple to constructor arguments. 02:55.330 --> 02:58.810 To do that, we need to call the function make_from_tuple(). 02:59.530 --> 03:01.000 This is a template function. 03:01.360 --> 03:03.130 The parameter is the class. 03:03.520 --> 03:06.130 So that is going to be the class whose constructor will be called. 03:06.730 --> 03:11.890 And then the argument is the tuple containing the arguments for the constructor call. 03:14.830 --> 03:17.350 So here is a class, or rather struct. 03:17.950 --> 03:20.800 It has a constructor, which takes int, double and string. 03:21.940 --> 03:23.770 Then we call make_from_tuple(). 03:24.490 --> 03:26.410 The parameter is this class. 03:26.830 --> 03:32.080 So this is going to call the class constructor. And it is going to pass the elements of this tuple as 03:32.080 --> 03:32.770 the arguments 03:33.100 --> 03:34.240 to that constructor call. 03:34.780 --> 03:37.990 So this is going to forward the tuple elements into the constructor. 03:40.760 --> 03:46.220 And then we just have a function which will print out the values of the members. So we can see if they have 03:46.220 --> 03:47.480 been correctly initialized. 03:48.770 --> 03:52.730 Visual Studio will not actually compile this code. Or, at least, not the version I have. 03:53.330 --> 04:02.450 So I am going to quickly switch over to MinGW. And, remember, we need to use the C++17 option for all 04:02.450 --> 04:03.230 these examples. 04:06.650 --> 04:09.920 So "i" is one, "d" is two and "s" is "three". 04:10.970 --> 04:16.730 So those are the values we would expect. So that has worked. That has correctly initialized the object 04:16.730 --> 04:19.550 from the tuple. OK, so that is it for this video. 04:19.940 --> 04:20.780 I will see you next time. 04:20.780 --> 04:22.820 But until then, keep coding!