Avoid dynamic parse method dispatch for faster access (#311)

On some benchmarks it seems to make a difference:

- `quoted` from `benchmark/parse.yaml`
- `quote_char_nil` from `benchmark/parse_quote_char_nil.yaml`

```
N_ROWS=5000 rake benchmark:parse benchmark:parse_liberal_parsing benchmark:parse_quote_char_nil benchmark:parse_strip
```
```
RUBYLIB= BUNDLER_ORIG_RUBYLIB= /Users/vladimirkochnev/.asdf/installs/ruby/3.3.3/bin/ruby -v -S benchmark-driver /Users/vladimirkochnev/code/csv/benchmark/parse.yaml
ruby 3.3.3 (2024-06-12 revision f1c7b6f435) [arm64-darwin23]
Calculating -------------------------------------
                      csv 3.3.0      master
            unquoted     22.147      22.131 i/s -     100.000 times in 4.515187s 4.518589s
              quoted     11.517      12.997 i/s -     100.000 times in 8.682986s 7.694298s
               mixed     14.097      13.964 i/s -     100.000 times in 7.093660s 7.161389s
     include_col_sep      5.214       5.188 i/s -     100.000 times in 19.178537s 19.277059s
     include_row_sep      5.195       5.101 i/s -     100.000 times in 19.250419s 19.605061s
        encode_utf-8     16.030      15.984 i/s -     100.000 times in 6.238449s 6.256427s
         encode_sjis     16.546      16.376 i/s -     100.000 times in 6.043603s 6.106603s

Comparison:
                         unquoted
           csv 3.3.0:        22.1 i/s
              master:        22.1 i/s - 1.00x  slower

                           quoted
              master:        13.0 i/s
           csv 3.3.0:        11.5 i/s - 1.13x  slower

                            mixed
           csv 3.3.0:        14.1 i/s
              master:        14.0 i/s - 1.01x  slower

                  include_col_sep
           csv 3.3.0:         5.2 i/s
              master:         5.2 i/s - 1.01x  slower

                  include_row_sep
           csv 3.3.0:         5.2 i/s
              master:         5.1 i/s - 1.02x  slower

                     encode_utf-8
           csv 3.3.0:        16.0 i/s
              master:        16.0 i/s - 1.00x  slower

                      encode_sjis
           csv 3.3.0:        16.5 i/s
              master:        16.4 i/s - 1.01x  slower

```
```
RUBYLIB= BUNDLER_ORIG_RUBYLIB= /Users/vladimirkochnev/.asdf/installs/ruby/3.3.3/bin/ruby -v -S benchmark-driver /Users/vladimirkochnev/code/csv/benchmark/parse_liberal_parsing.yaml
ruby 3.3.3 (2024-06-12 revision f1c7b6f435) [arm64-darwin23]
Calculating -------------------------------------
                                   csv 3.3.0      master
                         unquoted      8.132       8.250 i/s -     100.000 times in 12.297793s 12.121689s
         unquoted_backslash_quote      3.868       3.866 i/s -     100.000 times in 25.849956s 25.869413s
                           quoted      3.642       3.638 i/s -     100.000 times in 27.454032s 27.484247s
quoted_double_quote_outside_quote      2.277       2.202 i/s -     100.000 times in 43.921488s 45.419138s
           quoted_backslash_quote      1.801       1.803 i/s -     100.000 times in 55.522265s 55.464641s
                  include_col_sep      3.644       3.633 i/s -     100.000 times in 27.440353s 27.528626s
                  include_row_sep      3.629       3.614 i/s -     100.000 times in 27.559354s 27.670274s
                     encode_utf-8      8.149       8.136 i/s -     100.000 times in 12.270936s 12.290646s
                      encode_sjis      8.527       8.425 i/s -     100.000 times in 11.727969s 11.868855s

Comparison:
                                      unquoted
                           master:         8.2 i/s
                        csv 3.3.0:         8.1 i/s - 1.01x  slower

                      unquoted_backslash_quote
                        csv 3.3.0:         3.9 i/s
                           master:         3.9 i/s - 1.00x  slower

                                        quoted
                        csv 3.3.0:         3.6 i/s
                           master:         3.6 i/s - 1.00x  slower

             quoted_double_quote_outside_quote
                        csv 3.3.0:         2.3 i/s
                           master:         2.2 i/s - 1.03x  slower

                        quoted_backslash_quote
                           master:         1.8 i/s
                        csv 3.3.0:         1.8 i/s - 1.00x  slower

                               include_col_sep
                        csv 3.3.0:         3.6 i/s
                           master:         3.6 i/s - 1.00x  slower

                               include_row_sep
                        csv 3.3.0:         3.6 i/s
                           master:         3.6 i/s - 1.00x  slower

                                  encode_utf-8
                        csv 3.3.0:         8.1 i/s
                           master:         8.1 i/s - 1.00x  slower

                                   encode_sjis
                        csv 3.3.0:         8.5 i/s
                           master:         8.4 i/s - 1.01x  slower

```
```
RUBYLIB= BUNDLER_ORIG_RUBYLIB= /Users/vladimirkochnev/.asdf/installs/ruby/3.3.3/bin/ruby -v -S benchmark-driver /Users/vladimirkochnev/code/csv/benchmark/parse_quote_char_nil.yaml
ruby 3.3.3 (2024-06-12 revision f1c7b6f435) [arm64-darwin23]
Calculating -------------------------------------
                      csv 3.3.0      master
  without_quote_char     22.840      22.844 i/s -     100.000 times in 4.378284s 4.377488s
      quote_char_nil     32.370      43.729 i/s -     100.000 times in 3.089285s 2.286831s
       col_sep_space     12.135      12.106 i/s -     100.000 times in 8.240368s 8.260030s

Comparison:
               without_quote_char
              master:        22.8 i/s
           csv 3.3.0:        22.8 i/s - 1.00x  slower

                   quote_char_nil
              master:        43.7 i/s
           csv 3.3.0:        32.4 i/s - 1.35x  slower

                    col_sep_space
           csv 3.3.0:        12.1 i/s
              master:        12.1 i/s - 1.00x  slower

```
```
RUBYLIB= BUNDLER_ORIG_RUBYLIB= /Users/vladimirkochnev/.asdf/installs/ruby/3.3.3/bin/ruby -v -S benchmark-driver /Users/vladimirkochnev/code/csv/benchmark/parse_strip.yaml
ruby 3.3.3 (2024-06-12 revision f1c7b6f435) [arm64-darwin23]
Calculating -------------------------------------
                      csv 3.3.0      master
             default     13.132      13.043 i/s -     100.000 times in 7.615051s 7.667227s
      no_quote_strip      8.955       8.957 i/s -     100.000 times in 11.167272s 11.164189s

Comparison:
                          default
           csv 3.3.0:        13.1 i/s
              master:        13.0 i/s - 1.01x  slower

                   no_quote_strip
              master:         9.0 i/s
           csv 3.3.0:         9.0 i/s - 1.00x  slower

```

Author: marshall-lee

benchmark/convert_nil.yaml

@@ -4,6 +4,8 @@ contexts:
       csv: 3.0.1
   - gems:
       csv: 3.0.2
+  - gems:
+      csv: 3.3.0
   - name: "master"
     prelude: |
       $LOAD_PATH.unshift(File.expand_path("lib"))

benchmark/parse.yaml

@@ -4,6 +4,8 @@ contexts:
       csv: 3.0.1
   - gems:
       csv: 3.0.2
+  - gems:
+      csv: 3.3.0
   - name: "master"
     prelude: |
       $LOAD_PATH.unshift(File.expand_path("lib"))

benchmark/parse_liberal_parsing.yaml

@@ -2,6 +2,8 @@ loop_count: 100
 contexts:
   - gems:
       csv: 3.0.2
+  - gems:
+      csv: 3.3.0
   - name: "master"
     prelude: |
       $LOAD_PATH.unshift(File.expand_path("lib"))

benchmark/parse_quote_char_nil.yaml

@@ -1,5 +1,7 @@
 loop_count: 100
 contexts:
+  - gems:
+      csv: 3.3.0
   - name: "master"
     prelude: |
       $LOAD_PATH.unshift(File.expand_path("lib"))

benchmark/parse_strip.yaml

@@ -1,5 +1,7 @@
 loop_count: 100
 contexts:
+  - gems:
+      csv: 3.3.0
   - name: "master"
     prelude: |
       $LOAD_PATH.unshift(File.expand_path("lib"))

benchmark/read.yaml

@@ -4,6 +4,8 @@ contexts:
       csv: 3.0.1
   - gems:
       csv: 3.0.2
+  - gems:
+      csv: 3.3.0
   - name: "master"
     prelude: |
       $LOAD_PATH.unshift(File.expand_path("lib"))

benchmark/shift.yaml

@@ -4,6 +4,8 @@ contexts:
       csv: 3.0.1
   - gems:
       csv: 3.0.2
+  - gems:
+      csv: 3.3.0
   - name: "master"
     prelude: |
       $LOAD_PATH.unshift(File.expand_path("lib"))

benchmark/write.yaml

@@ -4,6 +4,8 @@ contexts:
       csv: 3.0.1
   - gems:
       csv: 3.0.2
+  - gems:
+      csv: 3.3.0
   - name: "master"
     prelude: |
       $LOAD_PATH.unshift(File.expand_path("lib"))

lib/csv/parser.rb

@@ -409,13 +409,7 @@ def parse(&block)
 
       begin
         @scanner ||= build_scanner
-        if quote_character.nil?
-          parse_no_quote(&block)
-        elsif @need_robust_parsing
-          parse_quotable_robust(&block)
-        else
-          parse_quotable_loose(&block)
-        end
+        __send__(@parse_method, &block)
       rescue InvalidEncoding
         if @scanner
           ignore_broken_line
@@ -459,7 +453,6 @@ def prepare
     end
 
     def prepare_variable
-      @need_robust_parsing = false
       @encoding = @options[:encoding]
       liberal_parsing = @options[:liberal_parsing]
       if liberal_parsing
@@ -472,7 +465,6 @@ def prepare_variable
           @double_quote_outside_quote = false
           @backslash_quote = false
         end
-        @need_robust_parsing = true
       else
         @liberal_parsing = false
         @backslash_quote = false
@@ -554,15 +546,13 @@ def prepare_strip
           @rstrip_value = Regexp.new(@escaped_strip +
                                      "+\\z".encode(@encoding))
         end
-        @need_robust_parsing = true
       elsif @strip
         strip_values = " \t\f\v"
         @escaped_strip = strip_values.encode(@encoding)
         if @quote_character
           @strip_value = Regexp.new("[#{strip_values}]+".encode(@encoding))
           @rstrip_value = Regexp.new("[#{strip_values}]+\\z".encode(@encoding))
         end
-        @need_robust_parsing = true
       end
     end
 
@@ -808,6 +798,13 @@ def adjust_headers(headers, quoted_fields)
 
     def prepare_parser
       @may_quoted = may_quoted?
+      if @quote_character.nil?
+        @parse_method = :parse_no_quote
+      elsif @liberal_parsing or @strip
+        @parse_method = :parse_quotable_robust
+      else
+        @parse_method = :parse_quotable_loose
+      end
     end
 
     def may_quoted?
@@ -987,7 +984,7 @@ def parse_quotable_loose(&block)
           quoted_fields = []
         elsif line.include?(@cr) or line.include?(@lf)
           @scanner.keep_back
-          @need_robust_parsing = true
+          @parse_method = :parse_quotable_robust
           return parse_quotable_robust(&block)
         else
           row = line.split(@split_column_separator, -1)
@@ -1011,7 +1008,7 @@ def parse_quotable_loose(&block)
                 row[i] = column[1..-2]
               else
                 @scanner.keep_back
-                @need_robust_parsing = true
+                @parse_method = :parse_quotable_robust
                 return parse_quotable_robust(&block)
               end
               validate_field_size(row[i])