Type Declarations

The first new feature I want to cover is type declarations. 0:00 This simply means specifying which type of variable is being set, 0:03 instead of allowing PHP to set this automatically. 0:07 PHP is considered a weak typed language. 0:10 In essence, this means that PHP does not require that you declare the data types. 0:14 Variables still have data types associated with them, but you can do radical things, 0:19 like adding a string to an integer without resulting in an error. 0:25 Type declarations can help you define what should occur, so 0:29 that you get the expected results. 0:33 This can also make your code easier to read. 0:35 We'll look at some specific examples shortly. 0:37 Since PHP5, you can use type hinting to specify the expected data types 0:40 of an argument in a function declaration, but only in the declaration. 0:46 When you call the function, PHP will check whether or 0:51 not the arguments are of the specified type. 0:54 If not, the runtime will raise an error and the execution will be halted. 0:57 Besides only being used in function declarations, 1:02 we are also limited to basically two types, a class name or an array. 1:06 Here's an example. 1:12 If we were to create a function for enrolling students, 1:14 we would require that the first argument be an object of the class, Student, and 1:17 the second argument to be an array of classes. 1:22 If we tried to pass just the name of the student instead of an object, 1:25 we would get a fatal error. 1:29 If we were to pass a single class instead of an array of classes, 1:31 we would also get an error. 1:35 We are required to pass a student object and an array. 1:38 If we were to try to check for a scalar variable, such as a string, PHP5 expects 1:43 it to be an object of the class, string, not the variable type, string. 1:49 With PHP7, we now have added scalar types. 1:55 Specifically, int, float, string, and bool. 1:59 By adding scalar type hints and enabling strict requirements, it is hoped 2:04 that more correct and self-documenting PHP programs can be written. 2:08 It also gives you more control over your code and can make the code easier to read. 2:13 By default, scalar type declarations are non-strict, which means they attempt 2:18 to change the original type to match the type specified in the type declaration. 2:24 In other words, if you pass a string that starts with a number into a function that 2:29 requires a float, it will grab the number from the beginning and 2:34 remove everything else. 2:39 Passing a float into a function that requires an int will become simply an int. 2:40 Let's look at an example of a non-strict type. 2:46 The getTotal function receives two floats and adds them together, 2:49 while it returns the sum. 2:53 Without strict types turned on, PHP attempts to cast or 2:55 to change these arguments to match the type specified in the function. 2:59 So when we call getTotal with non-strict types using an int of two and 3:03 a string of one week, PHP converts these to floats, the first argument 3:08 would be changed to 2.0, and the second argument would be changed to 1.0. 3:14 However, you will get a notice because this is not a well formed numeric value. 3:19 The function will then return a value of three, 3:23 which would be completely wrong if we were trying to add days. 3:26 When we call getTotal with the float 2.8 and the string of 3.2, 3:30 PHP converts the string to the float 3.2 with no notice, 3:35 because it was a smooth conversion. 3:39 It then returns a value of six. 3:43 When we call getTotal with non-strict types using the float 2.5, 3:45 and the integer 1, the integer gets converted to the float 1.0 and 3:51 the function returns 3.5. 3:56 Additionally, PHP7 gives us the opportunity to enable strict mode 3:58 on a file-by-file basis. 4:03 We do this by declaring strict types at the top of any given file. 4:06 This must be the very first line, even before name spaces. 4:10 Declaring strict typing will ensure that any function call made in that file 4:14 strictly adheres to the type specified. 4:19 Strict is determined by the file in which the call to the function is made, 4:22 not the file in which the function is defined. 4:27 If a type declaration mismatch occurs, a fatal error is thrown, and 4:29 we know that something is not functioning as desired. 4:34 Instead of allowing PHP to simply guess at what we want to happen, 4:36 allowing PHP to guess can cause seemingly random and hard to diagnose issues. 4:40 We'll look at catching and handling errors in the next section. 4:46 But for now, let's take a look at examples using strict types turned on. 4:49 When declare strict type has been turned on, 4:53 the first two calls that pass a string will produce a fatal error. 4:56 The exception to strict typing is shown in the third call. 5:00 If you pass an int as an argument that is looking for 5:03 a float, PHP will perform what is called widening, 5:07 by adding a dot zero to the end, and the function returns 3.5. 5:11 PHP7 also supports return type declarations, 5:16 which support all the same types as arguments. 5:19 To specify the return type, we add a colon, and then the type, 5:23 right before the opening curly bracket. 5:26 If we specify the return type of float, it will work exactly like it has been working 5:29 in the previous two examples, since the type being returned was already a float. 5:34 Adding the return types allows you to be sure that your function returns what 5:39 you expected to return, 5:44 as well as make int easy to see up front how the function works. 5:45 If we specify the return type as int without strict type set, 5:50 everything will work the same as it did without a return type. 5:54 The only difference is that it will force the return to be an int. 5:58 In the third call, the return value will truncate to three 6:01 because the floating point will be dropped. 6:05 If we turn strict types on, we'll get a fatal type error. 6:09 In this case, we'll need to specifically cast our return value as an int. 6:13 This will then return the truncated value. 6:18 The new type declarations can make code easier to read and 6:21 forces things to be used the way they were intended. 6:24 Some people prefer to use unit testing to check for intended use instead. 6:28 Having automated tests for your code is highly recommended, but 6:33 you can use both unit tests and type declarations working in harmony together. 6:36 Either way, PHP does not require that you declare types, but 6:41 it can definitely make code easier to read. 6:45 You can see right at the start of a function what is required and 6:49 what is returned. 6:52 When you are working with declared types with strict types turned on, 6:54 here are a few things to remember. 6:57 Strict types are enabled or disabled per file, not a php.ini setting. 7:00 Strict applies to the file in which the call to the function is made, 7:07 not the file in which the function is defined. 7:11 If strict is defined in test.php, 7:15 all function calls made from test.php have strict typing. 7:17 Integers will be widened into floats by adding dot zero. 7:22 All other type conversions will error. 7:26