Go Basic Syntax

Go language has simple and clear syntax. This chapter will detail the basic syntax rules of Go language, including identifiers, keywords, literals, operators, and other core concepts.

🔤 Identifiers

Identifier Rules

Identifiers in Go are used to name variables, types, functions, etc.

Naming Rules

1. Character Composition: Letters, numbers, underscores
2. First Character: Must be a letter or underscore
3. Case Sensitive: name and Name are different identifiers
4. Length Limit: No limit, but reasonable length is recommended

// Valid identifiers
var name string
var age int
var _private string
var userName string
var user_name string    // Not recommended, Go style prefers camelCase
var π float64          // Supports Unicode characters
var 中文变量 string      // Supports Chinese, but not recommended

// Invalid identifiers
// var 123name string   // Cannot start with number
// var my-name string   // Cannot contain hyphen
// var my name string   // Cannot contain space

Naming Conventions

Go Naming Conventions

// 1. Camel case (recommended)
var userName string      // Small camel, used within package
var UserName string      // Big camel, exported identifier

// 2. Constant naming
const MaxSize = 100      // Exported constant
const maxRetries = 3     // Package-internal constant

// 3. Function naming
func getName() string    // Package-internal function
func GetName() string    // Exported function

// 4. Type naming
type user struct         // Package-internal type
type User struct         // Exported type

// 5. Interface naming
type reader interface    // Package-internal interface
type Reader interface    // Exported interface

Visibility Rules

package example

// Exported (accessible from other packages)
var PublicVar = "Public variable"
func PublicFunc() {}
type PublicType struct {}

// Package-internal (accessible only within current package)
var privateVar = "Private variable"
func privateFunc() {}
type privateType struct {}

🔑 Keywords

Go Reserved Words

Go has 25 keywords that cannot be used as identifiers:

// Package and import
package  import

// Declaration
var      const    type     func

// Control flow
if       else     switch   case     default
for      range    break    continue goto
return   go       select   defer

// Type
chan     interface  map     struct

// Other
fallthrough

Keyword Categories

1. Declaration Keywords

package main      // Package declaration
import "fmt"      // Import declaration
var x int        // Variable declaration
const PI = 3.14  // Constant declaration
type Point struct { X, Y int }  // Type declaration
func hello() {}  // Function declaration

2. Control Flow Keywords

// Conditional control
if x > 0 {
    fmt.Println("Positive")
} else {
    fmt.Println("Non-positive")
}

// Multi-branch control
switch x {
case 1:
    fmt.Println("One")
case 2:
    fmt.Println("Two")
default:
    fmt.Println("Other")
}

// Loop control
for i := 0; i < 10; i++ {
    if i == 5 {
        continue  // Skip current iteration
    }
    if i == 8 {
        break     // Break out of loop
    }
    fmt.Println(i)
}

// Function return
func add(a, b int) int {
    return a + b
}

// Unconditional jump (not recommended)
goto label
label:
    fmt.Println("Jump here")

3. Concurrency Keywords

// Start goroutine
go func() {
    fmt.Println("Execute concurrently")
}()

// Channel operation
ch := make(chan int)
select {
case x := <-ch:
    fmt.Println("Received:", x)
case ch <- 42:
    fmt.Println("Sent successfully")
default:
    fmt.Println("No available operation")
}

// Deferred execution
func example() {
    defer fmt.Println("Execute at function end")
    fmt.Println("Normal execution")
}

💡 Literals

Numeric Literals

Integer Literals

// Decimal
var dec = 42
var dec2 = 1_000_000  // Can use underscores for readability

// Binary (Go 1.13+)
var bin = 0b1010      // Binary: 10

// Octal
var oct = 0o755       // Octal: 493
var oct2 = 0755       // Traditional octal notation

// Hexadecimal
var hex = 0xFF        // Hexadecimal: 255
var hex2 = 0x2A       // Hexadecimal: 42

Floating-Point Literals

// Decimal form
var f1 = 3.14
var f2 = .25          // 0.25
var f3 = 1.           // 1.0

// Scientific notation
var f4 = 1e6          // 1000000.0
var f5 = 2.5e-3       // 0.0025
var f6 = 1.5E+2       // 150.0

// Hexadecimal floating-point
var f7 = 0x1p-2       // 0.25 (1 * 2^-2)

String Literals

Interpreted Strings

// Use double quotes, supports escape characters
var str1 = "Hello, World!"
var str2 = "First line\nSecond line"
var str3 = "Tab\tseparated"
var str4 = "Quote: \"content\""
var str5 = "Backslash: \\"

Raw Strings

// Use backticks, does not process escape characters
var raw1 = `Hello, World!`
var raw2 = `First line
Second line`  // Preserves newline
var raw3 = `File path: C:\Program Files\Go\bin`
var raw4 = `Regular expression: \d+\.\d+`

Character Literals

// Use single quotes to represent characters (rune type)
var char1 = 'A'          // Character A
var char2 = '中'         // Chinese character
var char3 = '\n'         // Newline character
var char4 = '\u4e2d'     // Unicode: 中
var char5 = '\U00004e2d' // Unicode: 中
var char6 = '\x41'       // Hexadecimal: A

Boolean Literals

var true_val = true
var false_val = false

📝 Syntax Structure

Statement Separation

// Go automatically inserts semicolons, usually no need to add manually
fmt.Println("First statement")
fmt.Println("Second statement")

// Multiple statements on same line require semicolon separation (not recommended)
x := 1; y := 2; z := x + y

// Braces cannot be placed on a new line alone (syntax requirement)
if x > 0 {  // Correct
    fmt.Println("Positive")
}

// if x > 0    // Wrong! Semicolon will be inserted automatically
// {
//     fmt.Println("Positive")  
// }

Code Blocks

// Use braces to define code blocks
{
    var x = 1
    fmt.Println(x)
    // x is only accessible within this code block
}
// fmt.Println(x)  // Error! x is out of scope

// Function code block
func example() {
    // Function body
}

// Conditional code block
if condition {
    // if code block
} else {
    // else code block
}

🔧 Expressions and Operators

Arithmetic Operators

var a, b = 10, 3

fmt.Println(a + b)    // 13  Addition
fmt.Println(a - b)    // 7   Subtraction
fmt.Println(a * b)    // 30  Multiplication
fmt.Println(a / b)    // 3   Division (integer division)
fmt.Println(a % b)    // 1   Remainder

// Floating-point division
var x, y = 10.0, 3.0
fmt.Println(x / y)    // 3.3333333333333335

Comparison Operators

var a, b = 5, 10

fmt.Println(a == b)   // false  Equal
fmt.Println(a != b)   // true   Not equal
fmt.Println(a < b)    // true   Less than
fmt.Println(a <= b)   // true   Less than or equal
fmt.Println(a > b)    // false  Greater than
fmt.Println(a >= b)   // false  Greater than or equal

Logical Operators

var x, y = true, false

fmt.Println(x && y)   // false  Logical AND
fmt.Println(x || y)   // true   Logical OR
fmt.Println(!x)       // false  Logical NOT
fmt.Println(!y)       // true   Logical NOT

Bit Operators

var a, b uint = 12, 10  // Binary: 1100, 1010

fmt.Println(a & b)     // 8   Bitwise AND: 1000
fmt.Println(a | b)     // 14  Bitwise OR: 1110
fmt.Println(a ^ b)     // 6   Bitwise XOR: 0110
fmt.Println(^a)        // Bitwise NOT
fmt.Println(a << 2)    // 48  Left shift: 110000
fmt.Println(a >> 2)    // 3   Right shift: 11

Assignment Operators

var x = 10

x += 5    // x = x + 5  Result: 15
x -= 3    // x = x - 3  Result: 12
x *= 2    // x = x * 2  Result: 24
x /= 4    // x = x / 4  Result: 6
x %= 5    // x = x % 5  Result: 1

// Bitwise assignment
x = 12    // Reset
x &= 10   // x = x & 10
x |= 5    // x = x | 5
x ^= 3    // x = x ^ 3
x <<= 1   // x = x << 1
x >>= 2   // x = x >> 2

Increment/Decrement Operators

var i = 5

i++       // i = i + 1  Result: 6
i--       // i = i - 1  Result: 5

// Note: In Go, ++ and -- are statements, not expressions
// var j = i++  // Error! Cannot use this way
// var k = ++i  // Error! Go has no pre-increment

🎯 Operator Precedence

From highest to lowest priority:

Priority	Operators	Description
5	* / % << >> & &^	Multiplication, division, shift, bitwise AND
4	+ - `	^`
3	== != < <= > >=	Comparison operators
2	&&	Logical AND
1	`

Precedence Example

// Calculations with different priorities
result := 2 + 3 * 4        // 14  (3*4 calculated first)
result = (2 + 3) * 4       // 20  (use parentheses to change priority)

// Logical operator priority
condition := true || false && false  // true (false && false calculated first)
condition = (true || false) && false // false (parentheses change priority)

🔄 Type Inference

var Declaration Type Inference

// Explicit type specification
var name string = "Go"
var age int = 10

// Type inference
var name2 = "Go"        // Inferred as string
var age2 = 10           // Inferred as int
var pi = 3.14           // Inferred as float64
var isTrue = true       // Inferred as bool

Short Variable Declaration

// Use := for declaration and initialization
name := "Go"            // string
age := 25               // int
height := 1.75          // float64
isStudent := false      // bool

// Multiple variable declaration
x, y := 10, 20
a, b, c := 1, 2.5, "hello"

📋 Blank Identifier

Discarding Unused Values

// When function returns multiple values, use _ to discard unused values
value, _ := strconv.Atoi("123")  // Ignore error
_, err := fmt.Println("Hello")   // Ignore returned byte count

// Import package but don't use (only execute init function)
import _ "net/http/pprof"

// Check if type implements interface
var _ io.Writer = (*os.File)(nil)

🎯 Practical Example

Comprehensive Syntax Example

package main

import (
    "fmt"
    "math"
    "strconv"
    "strings"
)

func main() {
    // Variable declaration and type inference
    var message string = "Hello, Go!"
    count := 42
    pi := 3.14159
    isActive := true
    
    // String operations
    fmt.Println("Original message:", message)
    fmt.Println("Uppercase:", strings.ToUpper(message))
    fmt.Println("Length:", len(message))
    
    // Numeric operations
    fmt.Printf("Number: %d, Square: %d\n", count, count*count)
    fmt.Printf("π ≈ %.2f, Area: %.2f\n", pi, pi*math.Pow(5, 2))
    
    // Conditional judgment
    if count > 40 {
        fmt.Println("count greater than 40")
    }
    
    // Type conversion
    countStr := strconv.Itoa(count)
    fmt.Println("Number to string:", countStr)
    
    // Operator demonstration
    a, b := 15, 4
    fmt.Printf("%d + %d = %d\n", a, b, a+b)
    fmt.Printf("%d - %d = %d\n", a, b, a-b)
    fmt.Printf("%d * %d = %d\n", a, b, a*b)
    fmt.Printf("%d / %d = %d\n", a, b, a/b)
    fmt.Printf("%d %% %d = %d\n", a, b, a%b)
    
    // Bit operation demonstration
    x, y := uint(12), uint(10)
    fmt.Printf("Bit AND: %d & %d = %d\n", x, y, x&y)
    fmt.Printf("Bit OR: %d | %d = %d\n", x, y, x|y)
    fmt.Printf("Bit XOR: %d ^ %d = %d\n", x, y, x^y)
    
    // Logical operations
    fmt.Printf("true && false = %t\n", true && false)
    fmt.Printf("true || false = %t\n", true || false)
    fmt.Printf("!true = %t\n", !true)
}

🎓 Summary

In this chapter, we learned the basic syntax of Go language:

• ✅ Identifiers: Naming rules and visibility standards
• ✅ Keywords: 25 reserved words and their uses
• ✅ Literals: Numeric, string, character, boolean literals
• ✅ Operators: Arithmetic, comparison, logical, bitwise, assignment operators
• ✅ Syntax Structure: Statement separation, code blocks, expressions
• ✅ Type Inference: Automatic type inference mechanism

Mastering these basic syntaxes is an important foundation for further learning Go.

---

Next, we will learn Go Data Types to deeply understand Go's type system.

Syntax Tips

• Go language syntax is designed to be simple and clear, reducing unnecessary complexity
• Brace placement has strict requirements, left brace cannot be on a new line alone
• Use gofmt tool to automatically format code and maintain consistent code style