Lua:什么时候可以使用冒号语法? [英] Lua: When is it possible to use colon syntax?

问题描述

尽管我了解.和: 之间的基本基本区别，但我还没有完全了解何时Lua允许使用冒号语法.例如，类似的方法确实可以工作:

While I understand the basic difference between . and :, I haven't fully figured out when Lua allows to use the colon syntax. For instance, something like this does work:

s = "test"
-- type(s) is string.
-- so I can write a colon function for that type
function string:myFunc() 
  return #self 
end

-- and colon function calls are possible
s:myFunc()

但是，相同的模式似乎不适用于其他类型.例如，当我有一个table而不是string时:

However the same pattern does not seem to work for other types. For instance, when I have a table instead of a string:

t = {}
-- type(t) is table.
-- so I can write a colon function for that type
function table:myFunc() 
  return #self 
end

-- Surprisingly, a colon function call is not not possible!
t:myFunc() -- error: attempt to call method 'myFunc' (a nil value)
-- But the verbose dot call works
table.myFunc(t)

继续使用其他类型:

x = 1
-- type(x) is number.
-- So I was expecting that I can write a colon function 
-- for that type as well. However, in this case even this
-- fails: 
function number:myFunc() 
  return self 
end
-- error: attempt to index global 'number' (a nil value)

我目前正试图弄清这一点.结论

I'm currently trying to make sense of this. Is it correct to conclude that

• 某些类型(如string)允许结肠功能定义和结肠功能调用.
• table之类的其他类型仅允许进行结肠功能定义，而不允许进行结肠功能调用.
• 还有其他类型，例如number都不允许.

• certain types like string allow both colon-function-definitions and colon-function-calls.
• other types like table allow only colon-function-definitions but not colon-function-calls.
• yet other types like number allow neither.

这些差异的确切原因是什么?是否有所有类型的列表，显示它们支持的冒号语法类型? number案例是否有解决方法，允许编写例如x:abs()?

What exactly is the reason for these differences? Is there a list of all types, showing which type of colon-syntax they support? Is there maybe a workaround for the number case, allowing to write e.g. x:abs()?

推荐答案

string上的第一个示例之所以有效，是因为所有字符串共享相同的元表，并将其存储在名为string的表中.

The first example on string works because, all strings share the same metatable, and it's stored in the table named string.

来自 string :

字符串库在表string中提供了其所有功能.它还为__index字段指向string表的字符串设置一个元表.因此，您可以使用面向对象样式的字符串函数.例如，string.byte(s,i)可以写为s:byte(i).

The string library provides all its functions inside the table string. It also sets a metatable for strings where the __index field points to the string table. Therefore, you can use the string functions in object-oriented style. For instance, string.byte(s,i) can be written as s:byte(i).

---

table上的第二个示例不起作用，因为每个表都有其自己的元表，名为table的表只是表库所有功能的集合.

---

The second example on table doesn't work because, every table has its own metatable, the table named table is just a collection of all the functions of table library.

数字之类的类型默认情况下不支持metatable.

Types like numbers don't support metatable by default.

这篇关于Lua:什么时候可以使用冒号语法?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！