String คือลำดับตัวอักษร เป็นอ็อบเจ็กต์มีเมธอดมากมาย คู่มือเมธอดที่ใช้บ่อยและมีประโยชน์
1. String Length
"ruby".size # 4 (length เหมือนกัน)
2. Check Empty String
"".empty? # true # blank = empty หรือแค่ whitespace
3. String Interpolation
name = "Jesus"
puts "Hello #{name}"
puts "The total is #{1+1}" # code ภายใน interpolation ได้
เรียก to_s อัตโนมัติ
4. Extract Substring
string = "abc123" string[0,3] # "abc" (start index, length) string[3,3] # "123" string[0..-2] # "abc12" (range, -2 = ตัว'avant-dernier) string[0..2] = "" # replace/remove substring
5. Check If Contains Substring
string = "Today is Saturday"
string.include?("Saturday") # true
string.index("day") # 2 (หา partial word, คืน index)
6. Pad String
"1101".rjust(8, "0") # "00001101" (pad ซ้าย) "1111".ljust(8, "0") # "11110000" (pad ขวา)
7. Compare Ignoring Case
lang1 = "ruby"; lang2 = "Ruby" lang1.upcase == lang2.upcase # แนะนำวิธีนี้ # หรือ casecmp? (น้อยใช้)
8. Trim Whitespace
" test ".strip # "test" " test ".lstrip # "test " (ซ้าย) " test ".rstrip # " test" (ขวา)
9. Prefix & Suffix
"ruby programming".start_with?("ruby") # true
"ruby programming".end_with?("programming") # true
"bacon is expensive".delete_suffix(" is expensive") # "bacon" (Ruby 2.5+)
10. String → Array of Characters
"a b c d".split # ["a","b","c","d"] (default space)
"a,b,c,d".split(",") # ["a","b","c","d"] (CSV)
# CSV จริงควรใช้ CSV class จาก stdlib
11. Array → String
['a','b','c'].join # "abc"
['a','b','c'].join("-") # "a-b-c"
12. String → Integer
"49".to_i # 49 "a".to_i # 0 (ไม่มีตัวเลข)
13. Check If String Is Number
"123".match?(/\A-?\d+\Z/) # true "123bb".match?(/\A-?\d+\Z/) # false
Regex: เริ่มต้น (\A) optional dash (-?) ตัวเลข (\d+) จนจบ (\Z)
14. Append Characters (Concatenation)
string = "" string << "hello" << " " << "there" # "hello there" # อย่าใช้ += สร้าง string ใหม่ทุกครั้ง ช้า!
15. Iterate Characters
"rubyguides".each_char { |ch| puts ch }
"rubyguides".chars # ["r","u","b","y","g","u","i","d","e","s"]
16. Upper/Lowercase
"abcd".upcase # "ABCD" "ABCD".downcase # "abcd"
17. Multiline Strings
b = <<-STRING aaa bbb ccc STRING a = %Q(aaa bbb ccc )
18. Replace Text (gsub)
"We have many dogs".gsub("dogs", "cats") # "We have many cats"
"abccc".gsub("c", "") # "ab" (remove)
"We have 3 cats".gsub(/\d+/, "5") # "We have 5 cats" (regex)
"the lord of the rings".gsub(/\w+/) { |w| w.capitalize } # "The Lord Of The Rings" (block)
# sub = replace first match only, gsub = all matches
19. Remove Last Character
name = gets.chomp # ลบ \n
"abcd?".chomp("?") # "abcd" (Ruby 2.3+ optional arg)
20. Change Encodings
"abc".encoding # Encoding:UTF-8
"abc".force_encoding("UTF-8") # enforce encoding
21. Count Characters
"aaab".count("a") # 3
"aaab".count("b") # 1
22. Summary
เรียนรู้ string methods มากมาย: join/split, gsub, strip, interpolation, encoding, counting Bookmark และแชร์ให้เพื่อน Ruby developers!
