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Types

3:47 with Jay McGavren

Go is statically typed, meaning that Go knows what the types of your values are even at compile time, and can tell whether they're being used appropriately.

Go is statically typed, meaning that Go knows what the types of your values are even at compile time, and can tell whether they're being used appropriately.

fmt.Println("hello" + 527) // invalid operation: "hello" + 527 (mismatched types string and int)

This code will print the types of several Go values:

package main

import (
    "fmt"
    "reflect"
)

func main() {
    fmt.Println(reflect.TypeOf(1))                      // int
    fmt.Println(reflect.TypeOf(1.5))                    // float64
    fmt.Println(reflect.TypeOf("hello"))                // string
    fmt.Println(reflect.TypeOf(false))                  // bool
    fmt.Println(reflect.TypeOf(net.IPv4(127, 0, 0, 1))) // net.IPv4
    fmt.Println(reflect.TypeOf(time.Now()))             // time.Time
}

Go is statically typed. 0:00 This means that Go knows what the types of your values are, even at compile time. 0:01 And it can tell whether they're being used appropriately. 0:05 For example, in this program here, 0:08 we try to add the number 527 onto the string hello. 0:10 And before our program even compiles, we get an error. 0:14 Saying, cannot convert the string hello to the type int. 0:18 And, this operation is invalid, trying to add 527 to the value hello. 0:21 In some languages this would fail at run time, 0:27 possibly while you demoing your software to a user. 0:29 In Go, it fails at compile time, so 0:32 your development team knows about the problem immediately. 0:34 There are many built in types for numbers, 0:38 most of which are used only in special circumstances. 0:40 You should know they exist, so you're not surprised by them later. 0:43 So I'll describe them to you briefly, but 0:46 then you can forget all about most of them. 0:48 Because they're really only two numeric types you're 0:50 going to use on a regular basis. 0:53 For integers you have int, int8, int16, int32 and int64. 0:55 The numbers at the end of int8, int16, etc, are the number of bits, ones and 1:00 zeroes, that are used to store the number in memory. 1:05 The more bits a number takes up, the larger its maximum value can be. 1:08 int8 can only hold a maximum value of 127. 1:11 You'll get an error if you try to treat a larger number as an int8. 1:15 But int64 can hold a maximum value of over 9 quintillion. 1:18 Of course, using more bits means using more of your computer's memory. 1:23 But computers have so much RAM these days, 1:26 it's generally not worth it to use the smaller types, 1:29 since the risk of errors is increased from using a number that's too large. 1:31 The int types can hold negative or positive numbers, 1:35 but the uint types can hold only positive numbers. 1:38 Again, unless you have a specific reason to use a uint, 1:42 it's probably not worth the additional effort. 1:45 You can just use a int type instead. 1:47 int and uint types can only hold whole numbers. 1:50 For floating point numbers, 1:53 that is numbers with a decimal point, you'll want the float32 or float64 types.. 1:54 But as I said, you don't need to remember most of those numeric types. 2:00 By default, Go treats whole numbers as being of the int type, which is 2:04 the same as the int64 type, unless you're on an old 32 bit operating system. 2:08 And floating point numbers are treated as the float64 type. 2:12 We can confirm this by importing the reflect package and 2:16 calling its type of function on an integer and on a floating point number. 2:19 If we run this, it will output int for the integer and float64 for 2:24 the floating point number. 2:27 If you're using a different numeric type and you wanna do math or comparisons with 2:29 hard coded numbers, you'll have to convert your values to int or float64 first. 2:33 So unless you have a particular reason to do otherwise, you'll find 2:38 it's much more convenient to just use the int and float64 types in your programs. 2:41 Now let's add a string and a Boolean value and see what types those are. 2:46 So I'll say, reflect.TypeOf and we'll add a string, hello. 2:53 And then reflect.TypeOf and we'll do a Boolean value, false. 2:59 Save that, rerun it. 3:04 And we can see that in addition to the ints and the float64 from before, 3:06 we have a string, and a bool value, short for Boolean. 3:10 Those are the most frequently used built in types. 3:15 It's also possible to define additional types. 3:17 The Go Standard Library includes several packages that define types of their own. 3:20 For example, if we were to import the net and time packages, and 3:24 then create a new net.IPv4 instance, 3:28 or a new time object, and then print the types of those objects, 3:34 we would get net.IP as the output as well as time.Time. 3:39 Those are the types of those values that get created 3:45

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