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70 lines
2.4 KiB
Markdown
70 lines
2.4 KiB
Markdown
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Updating from 3.x to 4.x
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========================
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In middleclass 4.0 there is no global `Object` class any more. Classes created with `class(<name>)` don't have a superclass any more.
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If you need a global `Object` class, you must create it explicitly and then use it when creating new classes:
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```lua
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local Object = class('Object')
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...
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local MyClass = class('MyClass', Object)
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```
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If you are using a library which depends on the internal implementation of middleclass they might not work with middleclass 4.0. You might need to update those other libraries.
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Middleclass 4.0 comes with support for `__index` metamethod support. If your library manipulated the classes' `__instanceDict` internal attribute, you might do the same thing now using `__index` instead.
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Also note that the class method `:implements` has been removed.
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Updating from 2.x to 3.x
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========================
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Middleclass used to expose several global variables on the main scope. It does not do that anymore.
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`class` is now returned by `require 'middleclass'`, and it is not set globally. So you can do this:
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```lua
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local class = require 'middleclass'
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local MyClass = class('MyClass') -- works as before
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```
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`Object` is not a global variable any more. But you can get it from `class.Object`
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```lua
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local class = require 'middleclass'
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local Object = class.Object
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print(Object) -- prints 'class Object'
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```
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The public functions `instanceOf`, `subclassOf` and `includes` have been replaced by `Object.isInstanceOf`, `Object.static.isSubclassOf` and `Object.static.includes`.
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Prior to 3.x:
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```lua
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instanceOf(MyClass, obj)
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subclassOf(Object, aClass)
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includes(aMixin, aClass)
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```
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Since 3.x:
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```lua
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obj:isInstanceOf(MyClass)
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aClass:isSubclassOf(Object)
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aClass:includes(aMixin)
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```
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The 3.x code snippet will throw an error if `obj` is not an object, or if `aClass` is not a class (since they will not implement `isInstanceOf`, `isSubclassOf` or `includes`).
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If you are unsure of whether `obj` and `aClass` are an object or a class, you can use the methods in `Object`. They are prepared to work with random types, not just classes and instances:
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```lua
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Object.isInstanceOf(obj, MyClass)
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Object.isSubclassOf(aClass, Object)
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Object.includes(aClass, aMixin)
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```
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Notice that the parameter order is not the same now as it was in 2.x. Also note the change in naming: `isInstanceOf` instead of `instanceOf`, and `isSubclassOf` instead of `subclassOf`.
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