jString变量在ruby的inject(又名reduce)中被强制转换为fixnum

Question

下面的代码将收集器变量"sql"作为字符串开始，但随后强制转换为固定值。没有明显的理由进行这样的转换。

segs=['segment1', 'segment2']
sx=1
sqlout = segs.inject("select ") do | sql, seg|
  puts "class of sql: #{sql.class}"
  salias = "#{seg.slice(1,3)}"
  if sx > 1 then sql <<= " ," end    # this if the offending line 8
  sql <<= "#{salias}.score as #{seg}_score"
  puts "class of sql at end: #{sql.class}"
  sx+=1
end

结果为

class of sql: String
class of sql at end: String
class of sql: Fixnum
TypeError: can't convert String into Integer
      << at org/jruby/RubyBignum.java:751
      << at org/jruby/RubyFixnum.java:1155
  (root) at ./pivot.rb:8
    each at org/jruby/RubyArray.java:1613
  inject at org/jruby/RubyEnumerable.java:820
  (root) at ./pivot.rb:5

Answer 1

您在inject中返回错误的值。下面的代码应该可以工作

segs=['segment1', 'segment2']
sx=1
sqlout = segs.inject("select ") do | sql, seg|
  puts "class of sql: #{sql.class}"
  salias = "#{seg.slice(1,3)}"
  if sx > 1 then sql <<= " ," end    # this if the offending line 8
  sql <<= "#{salias}.score as #{seg}_score"
  puts "class of sql at end: #{sql.class}"
  sx+=1
  sql
end

请记住，inject中的下一个输入是块的返回，而不是传递的第一个变量。

结果:

class of sql: String
class of sql at end: String
class of sql: String
class of sql at end: String