耙異常管理

Question

考慮這個Rake任務：

namespace :foo do 
    task :bar do 
    begin 
     raise 'foo' 
    rescue RuntimeError => ex 
     raise ex.class, 'bar', ex.backtrace 
    end 
    end 
end 

這將產生以下的輸出：

rake aborted! 
bar 
/home/vagrant/proj/lib/tasks/foo.rake:52:in `block (2 levels) in <top (required)>' 
/home/vagrant/.gem/ruby/2.3.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:268:in `load' 
/home/vagrant/.gem/ruby/2.3.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:268:in `block in load' 
/home/vagrant/.gem/ruby/2.3.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:240:in `load_dependency' 
/home/vagrant/.gem/ruby/2.3.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:268:in `load' 
-e:1:in `<main>' 
foo 
/home/vagrant/proj/lib/tasks/foo.rake:52:in `block (2 levels) in <top (required)>' 
/home/vagrant/.gem/ruby/2.3.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:268:in `load' 
/home/vagrant/.gem/ruby/2.3.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:268:in `block in load' 
/home/vagrant/.gem/ruby/2.3.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:240:in `load_dependency' 
/home/vagrant/.gem/ruby/2.3.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:268:in `load' 
-e:1:in `<main>' 
Tasks: TOP => foo:bar 
(See full trace by running task with --trace) 

正如你可以看到，有兩個原異常（foo）以及新的（bar）。 這是爲什麼？我曾預料foo例外已被妥善解救，不會在這裏出現。

Answer 1

這裏不是最初的例外（foo）。

Rake文件：

namespace :foo do 
    task :bar do 
    begin 
     raise "message from foo" 
    rescue RuntimeError => ex 
     puts "#{ex.message}. foo is rescued"    # <= 1st 
     raise ex.class, 'message from bar', ex.backtrace # <= 2nd 
    end 
    end 
end 

輸出：

message from foo. foo is rescued # <= 1st 
rake aborted! 
message from bar # <= 2nd 
/home/vagrant/Rakefile:4:in `block (2 levels) in <top (required)>' 
message from foo # <= from backtrace 
/home/vagrant/Rakefile:4:in `block (2 levels) in <top (required)>' 
Tasks: TOP => foo:bar 
(See full trace by running task with --trace)