Load

首先我們先建立三個檔案a.rb, b.rb, c.rb如下：

A = "A constant in a.rb"
p "Print A = '#{A}' in a.rb"

A = "A constant in b.rb"
p "Print A = '#{A}' in b.rb"

如果在c.rb裡同時load a.rb與b.rb兩個檔案：

load("a.rb")
load("b.rb")
p "Print A = '#{A}' in c.rb"
load("b.rb")

則會出現下面的結果：

"Print A = 'A constant in file a.rb' in a.rb"
b.rb:1: warning: already initialized constant A
a.rb:1: warning: previous definition of A was here
"Print A = 'A constant in file b.rb' in b.rb"
"Print A = 'A constant in file b.rb' in c.rb"
b.rb:1: warning: already initialized constant A
b.rb:1: warning: previous definition of A was here
"Print A = 'A constant in file b.rb' in b.rb"

由此可知，使用load有下面特性：

• 被load的檔案會被執行(print有被執行)。
• 如果load的兩個檔案裡有相同的constant，則會出現警告，而且會以最後載入的constant為主。
• 如果重複load相同的檔案，則檔案會被重複執行。

如果不想將b.rb裡的constant載入到c.rb中，則可以在load後面加上true：

load("a.rb")
load("b.rb", true)
p "Print A = '#{A}' in c.rb"

"Print A = 'A constant in file a.rb' in a.rb"
"Print A = 'A constant in file b.rb' in b.rb"
"Print A = 'A constant in file a.rb' in c.rb"

上面執行的結果就只會讀到a.rb的A，但b.rb的程式碼仍會執行。

Require

如果將c.rb改成require如下：

require("./a")
require("./b")
p "Print A = '#{A}' in c.rb"
require("./b")

則結果會變成：

"Print A = 'A constant in file a.rb' in a.rb"
/Users/kait/temp/b.rb:1: warning: already initialized constant A
/Users/kait/temp/a.rb:1: warning: previous definition of A was here
"Print A = 'A constant in file b.rb' in b.rb"
"Print A = 'A constant in file b.rb' in c.rb"

由此可知，require與load的差別在於

• require需要指定絕對路徑(更精確來說，如果不指定絕對路徑，則預設會去找$LOAD_PATH目錄裡有沒有指定的檔案，範例是將a.rb, b.rb, c.rb放在同一個目錄下，而./並不在預設的$LOAD_PATH，所以不加./會找不到)
• require可以省略檔案的副檔名.rb，但load則是一定要加.rb，不然會找不到檔案。
• 如果require兩次相同的檔案，則檔案只會載入並執行第一次，之後的不會重複載入執行，load則每次都會載入執行。