Perl的環境設置沒有影響

Question

package A; 
$ENV{MOJO_USERAGENT_DEBUG} =1; 
use Test::Mojo; 
use utf8; 

.... 
; 
1; 
package B; 
BEGIN{ $ENV{MOJO_USERAGENT_DEBUG =1 } }; 
use Test::Mojo; 
use utf8; 
... 
; 
1; 

的Test::Mojo包進口Mojo::UserAgent模塊：

package Test::Mojo; 
... 
use Mojo::UserAgent; 
... 
1; 

爲什麼代碼包A，不能打開調試。但包B可以嗎？

Answer 1

#!/usr/bin/env perl 
# vim:set shiftwidth=4 tabstop=4 expandtab ai smartindent fileformat=unix fileencoding=utf-8 syntax=perl: 
# http://perldoc.perl.org/perlmod.html#BEGIN,-UNITCHECK,-CHECK,-INIT-and-END 
package init; 
      { print "10. Ordinary code runs at runtime.\n"; } 
END   { print "16. So this is the end of the tale.\n" } 
INIT  { print " 7. INIT blocks run FIFO just before runtime.\n" } 
UNITCHECK { print " 4. And therefore before any CHECK blocks.\n" } 
CHECK  { print " 6. So this is the sixth line.\n" } 
      { print "11. It runs in order, of course.\n"; } 
BEGIN  { print " 1. BEGIN blocks run FIFO during compilation.\n" } 
END   { print "15. Read perlmod for the rest of the story.\n" } 
CHECK  { print " 5. CHECK blocks run LIFO after all compilation.\n" } 
INIT  { print " 8. Run this again, using Perl's -c switch.\n" } 
      { print "12. This is anti-obfuscated code.\n"; } 
END   { print "14. END blocks run LIFO at quitting time.\n" } 
BEGIN  { print " 2. So this line comes out second.\n" } 
UNITCHECK { print " 3. UNITCHECK blocks run LIFO after each file is compiled.\n" } 
INIT  { print " 9. You'll see the difference right away.\n" } 
      { print "13. It merely _looks_ like it should be confusing.\n"; } 
sub import { 
    print "IMPORT\n"; 
} 
1; 

這應該使它很清楚;-)。

換句話說：BEGIN塊和「使用」語句在相同的編譯步驟中以及它們出現的順序進行評估。在這兩個例子中BEGIN和「use」已經互換，所以在BEGIN塊中的「使用Test :: Mojo」後執行。我的猜測是Test :: Mojo在編譯時評估env var。如果它會在運行時評估它，它應該工作。

更多詳細資料？ see here。

Answer 2

由於Test :: Mojo在加載變量時會檢查變量，因此需要在此之前設置環境。