WEBVTT 00:00.280 --> 00:06.790 If a function calculates a value that can be calculated at compile time, you can mark it on the left 00:06.790 --> 00:08.890 of the declaration with the. 00:09.340 --> 00:14.530 For example, const expression here like this. 00:15.460 --> 00:23.020 Here with this the you're going to indicate that the compiler can optimize the code by computing the 00:23.020 --> 00:25.000 value at a compile time. 00:25.060 --> 00:30.180 So if the function value can be calculated at compile time, it means that the parameters in the function 00:30.230 --> 00:34.330 function call must be value can be calculated at compile time. 00:34.330 --> 00:42.100 So it means that the parameters, uh, in the function must be known at compile time and so they must 00:42.100 --> 00:42.970 be literal. 00:42.970 --> 00:45.190 So the function must also be single line. 00:45.190 --> 00:53.050 So if there is, if these restrictions are not met, then the compiler is free to ignore, uh, the 00:53.050 --> 00:53.920 specifier. 00:53.920 --> 01:00.130 But if you just compile it, the compiler won't say nothing here, but probably it will ignore the if 01:00.230 --> 01:03.920 these restrictions are not met. 01:04.280 --> 01:12.380 Uh, so the related in this inline specifier that, uh, this can be placed on the left of a function 01:12.380 --> 01:13.190 here. 01:13.870 --> 01:14.650 Inline. 01:15.760 --> 01:18.280 This can replaced the left of a function. 01:18.600 --> 01:24.470 Function declaration as a suggestion to the compiler that when other code call. 01:24.490 --> 01:30.730 Calls this function rather than rather than the compiler inserting a jump to the function in memory, 01:30.820 --> 01:36.290 the compiler should put a copy of the actual code in the calling function. 01:36.310 --> 01:43.840 Again, the compiler is free to ignore specifiers if this restrictions is not met. 01:44.800 --> 01:45.390 Here. 01:45.400 --> 01:48.880 So we're going to determine the return type here. 01:48.880 --> 01:54.720 So the functions may be written to run a routine and not a return value. 01:54.730 --> 02:02.740 So if this case this is the case, you must specify that the function returns the void here. 02:02.770 --> 02:03.580 Void here. 02:03.580 --> 02:08.380 But in this case, you're going to see error because we are returning something, right? 02:08.380 --> 02:11.170 So in most cases, a function will return a value. 02:11.170 --> 02:16.360 So if only indicate that the function has completed correctly. 02:16.360 --> 02:22.270 So there's no requirement that the calling function obtains the return value or does anything with it. 02:22.270 --> 02:27.610 So the calling function can simply ignore the return value. 02:27.610 --> 02:32.380 So there are two types, two ways to specify the return type. 02:32.680 --> 02:37.540 The first way is to give the type before the function name like this. 02:38.140 --> 02:44.930 In this case, this is an integer that returns integer, and this is the method used in most examples 02:44.930 --> 02:46.290 in this course so far. 02:46.310 --> 02:55.160 The second way is calling the trailing return type and requires that you place auto here auto as a return 02:55.160 --> 03:04.460 type before the function function name as and use the this syntax here like this. 03:05.940 --> 03:06.840 Integer. 03:06.870 --> 03:14.160 We use the syntax to give the actual return type after the parameter list. 03:14.160 --> 03:15.060 So. 03:16.030 --> 03:17.410 Uh, this function is so simple. 03:17.410 --> 03:20.440 That is a good candidate to be inlined. 03:20.440 --> 03:27.100 So the return type on the left is given auto here, meaning that the actual return type is specified 03:27.100 --> 03:31.120 after the parameter list and this operator. 03:31.120 --> 03:35.800 And it means that the return type is an integer. 03:35.800 --> 03:40.690 And this syntax has the same effect as using the integer on the left. 03:40.690 --> 03:41.230 So. 03:41.230 --> 03:42.110 But this is nice. 03:42.110 --> 03:47.710 This is useful when a function is templated and the return type may not be noticeable here. 03:47.710 --> 03:55.210 So in this trivial example, you can omit the return type entirely and just use the auto on the left 03:55.210 --> 03:56.560 of the function name. 03:56.560 --> 04:02.920 So this syntax means that the compiler will deduce the return type from the actual value returned. 04:02.920 --> 04:10.210 So clearly the compiler will know, will only know what return type is from the function body, so you 04:10.210 --> 04:14.350 can not provide a prototype for such functions. 04:14.350 --> 04:20.870 So finally, if a function does not return at all, for example, if it goes into a never ending loop 04:20.870 --> 04:23.600 to pull some value. 04:23.810 --> 04:33.740 So if it does not return a value at all, you can mark it with the C plus plus 11 attribute, the no 04:33.740 --> 04:44.000 return, no return attribute with this here so the compiler can use this attribute to read write more 04:44.000 --> 04:50.360 efficient code because it knows that the it does not need to provide the return value here.