字符串變量強制轉化爲fixnum裏面注入（aka reduce）爲ruby

Question

下面的代碼將收集器變量「sql」作爲字符串開始生命，然後強制轉換爲fixnum。這種轉換沒有明顯的理由。

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 

的結果是

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

您正在重返inject錯誤的值。以下應工作

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 

記得在inject下一個輸入是塊的回報，沒有通過第一個變量。

結果：

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