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.

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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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Types