WoW:Common Lua shortcuts - Revision history

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Move page script moved page Common Lua shortcuts to Common Lua shortcuts without leaving a redirect

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Bear at 09:18, 21 May 2020

2020-05-21T09:18:00Z

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	{{~~UIHowTo~~}}		{{wow/uihowto}}
	This article covers several syntactic features of Lua that are commonly used in addon code.		This article covers several syntactic features of Lua that are commonly used in addon code.

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	The [[API getglobal\|getglobal]]("name") function enables similar behavior, but at a marginally higher cost.		The [[API getglobal\|getglobal]]("name") function enables similar behavior, but at a marginally higher cost.

	[[Category:Interface customization]]		[[Category:Interface customization]]

WoWWiki>Sesshu: /* Logical short-cut evaluation */

2009-07-06T20:39:21Z

Logical short-cut evaluation

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	For instance:		For instance:
	MySVTable = MySVTable or {};		MySVTable = MySVTable or {};
	print(UnitExists("target") and "You have a target" or "You don't have a target")); -- As a trigraph		print(UnitExists("target") and "You have a target" or "You don't have a target"); -- As a trigraph

	A notable limitation of using short-cut evaluation as a trigraph operator is that if the ''true'' expression may return a false value, the false expression will be returned:		A notable limitation of using short-cut evaluation as a trigraph operator is that if the ''true'' expression may return a false value, the false expression will be returned:

WoWWiki>Fandyllic at 04:53, 13 March 2009

2009-03-13T04:53:48Z

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	print(UnitExists("target") and "You have a target" or "You don't have a target")); -- As a trigraph		print(UnitExists("target") and "You have a target" or "You don't have a target")); -- As a trigraph

	A notable limitation of using short-cut evaluation as a trigraph ~~oeprator~~ is that if the ''true'' expression may return a false value, the false expression will be returned:		A notable limitation of using short-cut evaluation as a trigraph operator is that if the ''true'' expression may return a false value, the false expression will be returned:
	function isFrameShown(frame, checkParentFrames)		function isFrameShown(frame, checkParentFrames)
	-- The expression below returns the wrong value if frame's parent is hidden.		-- The expression below returns the wrong value if frame's parent is hidden.
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	The [[API getglobal\|getglobal]]("name") function enables similar behavior, but at a marginally higher cost.		The [[API getglobal\|getglobal]]("name") function enables similar behavior, but at a marginally higher cost.

			[[Category:Interface customization]]

WoWWiki>Starlightblunder: Merge Tricks with Lua Doing Tricks Without Lua Method Notation Doing Tricks With Lua Method Notation

2009-03-12T18:20:35Z

Merge Tricks with Lua Doing Tricks Without Lua Method Notation Doing Tricks With Lua Method Notation

New page

{{UIHowTo}}
This article covers several syntactic features of Lua that are commonly used in addon code.

== Logical short-cut evaluation ==
When evaluating the results of boolean operators '''and''' and '''or''', Lua only evaluates the right-hand operand if necessary. This makes it possible to provide default values to nil or false expressions, or implement something resembling a trigraph operator.

For instance:
MySVTable = MySVTable or {};
print(UnitExists("target") and "You have a target" or "You don't have a target")); -- As a trigraph

A notable limitation of using short-cut evaluation as a trigraph oeprator is that if the ''true'' expression may return a false value, the false expression will be returned:
function isFrameShown(frame, checkParentFrames)
-- The expression below returns the wrong value if frame's parent is hidden.
return checkParentFrames and frame:IsVisible() or frame:IsShown();
end
This occurs because nothing prevents the evaluation of the or operator as its left-hand operand is false/nil.

== Colon syntax for defining methods ==
The colon syntax is used for defining methods -- functions that have an implicit first parameter ''self''. The following function definitions are equivalent:
t = {};
function t:foo(bar) end
function t.foo(self, bar) end

When you call a function using the colon syntax, you implicitly supply the table left of the colon as the first argument to the function. The following two function calls are equivalent:
t:foo("baz");
t.foo(t, "baz");

This notation is frequently used to emulate something resembling objects.

== The global environment table ==
The global environment table <code>_G</code> is defined in most function environments. You can look up global variables by using their names as a key in this table. For example:
-- Suppose MyBar1, MyBar2, MyBar3 are global variables (Frames created in XML, for example)
for i=1, 3 do
_G["MyBar" .. i]:Show();
end

The [[API getglobal|getglobal]]("name") function enables similar behavior, but at a marginally higher cost.