Logs, Logs, Logs!
Logs, Logs, Logs!

Logs, Logs, Logs!

Learning Exercise


The rune type in Go is an alias for int32. Given this underlying int32 type, the rune type holds a signed 32-bit integer value. However, unlike an int32 type, the integer value stored in a rune type represents a single Unicode character.

Unicode and Unicode Code Points

Unicode is a superset of ASCII that represents characters by assigning a unique number to every character. This unique number is called a Unicode code point. Unicode aims to represent all the world's characters including various alphabets, numbers, symbols, and even emoji as Unicode code points.

In Go, the rune type represents a single Unicode code point.

The following table contains example Unicode characters along with their Unicode code point and decimal values:

Unicode Character Unicode Code Point Decimal Value
0 U+0030 48
A U+0041 65
a U+0061 97
ยฟ U+00BF 191
ฯ€ U+03C0 960
๐Ÿง  U+1F9E0 129504


UTF-8 is a variable-width character encoding that is used to encode every Unicode code point as 1, 2, 3, or 4 bytes. Since a Unicode code point can be encoded as a maximum of 4 bytes, the rune type needs to be able to hold up to 4 bytes of data. That is why the rune type is an alias for int32 as an int32 type is capable of holding up to 4 bytes of data.

Go source code files are encoded using UTF-8.

Using Runes

Variables of type rune are declared by placing a character inside single quotes:

myRune := 'ยฟ'

Since rune is just an alias for int32, printing a rune's type will yield int32:

myRune := 'ยฟ'
fmt.Printf("myRune type: %T\n", myRune)
// Output: myRune type: int32

Similarly, printing a rune's value will yield its integer (decimal) value:

myRune := 'ยฟ'
fmt.Printf("myRune value: %v\n", myRune)
// Output: myRune value: 191

To print the Unicode character represented by the rune, use the %c formatting verb:

myRune := 'ยฟ'
fmt.Printf("myRune Unicode character: %c\n", myRune)
// Output: myRune Unicode character: ยฟ

To print the Unicode code point represented by the rune, use the %U formatting verb:

myRune := 'ยฟ'
fmt.Printf("myRune Unicode code point: %U\n", myRune)
// Output: myRune Unicode code point: U+00BF

Runes and Strings

Strings in Go are encoded using UTF-8 which means they contain Unicode characters. Since the rune type represents a Unicode character, a string in Go is often referred to as a sequence of runes. However, runes are stored as 1, 2, 3, or 4 bytes depending on the character. Due to this, strings are really just a sequence of bytes. In Go, slices are used to represent sequences and these slices can be iterated over using range.

Even though a string is just a slice of bytes, the range keyword iterates over a string's runes, not its bytes. In this example, the index variable represents the starting index of the current rune's byte sequence and the char variable represents the current rune:

myString := "โ—hello"
for index, char := range myString {
  fmt.Printf("Index: %d\tCharacter: %c\t\tCode Point: %U\n", index, char, char)
// Output:
// Index: 0	Character: โ—		Code Point: U+2757
// Index: 3	Character: h		Code Point: U+0068
// Index: 4	Character: e		Code Point: U+0065
// Index: 5	Character: l		Code Point: U+006C
// Index: 6	Character: l		Code Point: U+006C
// Index: 7	Character: o		Code Point: U+006F

Since runes can be stored as 1, 2, 3, or 4 bytes, the length of a string may not always equal the number of characters in the string. Use the builtin len function to get the length of a string in bytes and the utf8.RuneCountInString function to get the number of runes in a string:

import "unicode/utf8"

myString := "โ—hello"
stringLength := len(myString)
numberOfRunes := utf8.RuneCountInString(myString)

fmt.Printf("myString - Length: %d - Runes: %d\n", stringLength, numberOfRunes)
// Output: myString - Length: 8 - Runes: 6


You have been tasked with creating a log library to assist with managing your organization's logs. This library will allow users to identify which application emitted a given log, to fix corrupted logs, and to determine if a given log line is within a certain character limit.

1. Identify which application emitted a log

Logs come from multiple applications that each use their own proprietary log format. The application emitting a log must be identified before it can be stored in a log aggregation system.

Implement the Application function that takes a log line and returns the application that emitted the log line.

To identify which application emitted a given log line, search the log line for a specific character as specified by the following table:

Application Character Unicode Code Point
recommendation โ— U+2757
search ๐Ÿ” U+1F50D
weather โ˜€ U+2600

If a log line does not contain one of the characters from the above table, return default to the caller. If a log line contains more than one character in the above table, return the application corresponding to the first character found in the log line starting from left to right.

Application("โ— recommended search product ๐Ÿ”")
// => recommendation

2. Fix corrupted logs

Due to a rare but persistent bug in the logging infrastructure, certain characters in logs can become corrupted. After spending time identifying the corrupted characters and their original value, you decide to update the log library to assist in fixing corrupted logs.

Implement the Replace function that takes a log line, a corrupted character, and the original value and returns a modified log line that has all occurrences of the corrupted character replaced with the original value.

log := "please replace '๐Ÿ‘Ž' with '๐Ÿ‘'"

Replace(log, '๐Ÿ‘Ž', '๐Ÿ‘')
// => please replace '๐Ÿ‘' with '๐Ÿ‘'"

3. Determine if a log can be displayed

Systems responsible for displaying logs have a limit on the number of characters that can be displayed per log line. As such, users are asking for this library to include a helper function to determine whether or not a log line is within a specific character limit.

Implement the WithinLimit function that takes a log line and character limit and returns whether or not the log line is within the character limit.

WithinLimit("helloโ—", 6)
// => true
Edit via GitHub The link opens in a new window or tab
Go Exercism

Ready to start Logs, Logs, Logs!?

Sign up to Exercism to learn and master Go with 34 concepts, 140 exercises, and real human mentoring, all for free.