Hier werden die Unterschiede zwischen zwei Versionen angezeigt.
Beide Seiten der vorigen Revision Vorhergehende Überarbeitung Nächste Überarbeitung | Vorhergehende Überarbeitung | ||
becki:linux:lua [2014-08-20 13:21] becki |
becki:linux:lua [2023-12-27 13:57] (aktuell) becki [Classes and Objects] |
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* [[http://lua-users.org/wiki/LibrariesAndBindings|Manual]] | * [[http://lua-users.org/wiki/LibrariesAndBindings|Manual]] | ||
- | ===== Standalone lua == | + | ===== Implementations == |
- | ==== Shebang == | + | ==== Standalone lua == |
+ | === Shebang == | ||
''#!/usr/bin/lua'' | ''#!/usr/bin/lua'' | ||
- | ==== Command Line Arguments == | + | === Command Line Arguments == |
Use global table ''arg'' | Use global table ''arg'' | ||
- | ==== StdIo == | + | === StdIo == |
<code lua> | <code lua> | ||
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io.stderr:write() -- Print a string to stderr | io.stderr:write() -- Print a string to stderr | ||
</code> | </code> | ||
+ | |||
+ | ==== Lua for Web Browsers == | ||
+ | |||
+ | [[http://kripken.github.io/lua.vm.js/script_example.html|lua.vm.js]] thanks to asm.js | ||
+ | |||
+ | ==== Lua for Java/Android == | ||
+ | |||
+ | [[https://sourceforge.net/projects/luaj/|Luaj]], seen at [[https://github.com/M66B/XPrivacyLua/blob/master/README.md|XPrivacyLua]] | ||
===== C-style ?-operator equivalent == | ===== C-style ?-operator equivalent == | ||
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d1, d2 = table.unpack(a and {b1, b2} or {c1, c2}) | d1, d2 = table.unpack(a and {b1, b2} or {c1, c2}) | ||
</code> | </code> | ||
+ | |||
+ | <note warning>Take care if b can become ''nil'' or ''false''. In this case the equivalent doesn't work. Instead use:</note> | ||
+ | <code lua> | ||
+ | if a then d=b else d=c end | ||
+ | </code> | ||
+ | |||
+ | ===== Default values for missing arguments == | ||
+ | |||
+ | <code lua> | ||
+ | function foo(a) | ||
+ | a= a or "defaultvalue" | ||
+ | end | ||
+ | </code> | ||
+ | |||
+ | Take care, if ''false'' is a valid value, instead use: | ||
+ | |||
+ | <code lua> | ||
+ | function foo(a) | ||
+ | if a==nil then a="defaultvalue" end | ||
+ | end | ||
+ | </code> | ||
+ | |||
===== Difference between nil and no value == | ===== Difference between nil and no value == | ||
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<note warning>An example for a function returning nothing is the result of string.gmatch()</note> | <note warning>An example for a function returning nothing is the result of string.gmatch()</note> | ||
+ | |||
+ | ===== Lexical scoping == | ||
+ | |||
+ | <code lua> | ||
+ | local strict= require"fs.strict" | ||
+ | local g,h,i | ||
+ | |||
+ | local function f() | ||
+ | g() -- ok | ||
+ | h() -- ok | ||
+ | --i() -- err, because i refers to old upvalue which is still nill | ||
+ | end | ||
+ | |||
+ | g= function() end -- existing upvalue g is assigned a function | ||
+ | function h() end -- same as above (mind the missing "local"!) | ||
+ | local function i() end -- a new upvalue is created which hides old i(assumption) | ||
+ | |||
+ | f() | ||
+ | i() -- ok | ||
+ | </code> | ||
===== Numeric for Loop == | ===== Numeric for Loop == | ||
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===== Classes and Objects == | ===== Classes and Objects == | ||
+ | |||
+ | See also projects/accounting/sbaccimport which has since rev 482:c85c255f1870 classes with inheritance where the constructor new() is a class method and can therefore be reused in child classes similar to PIL capter 21 | ||
==== Classes as Object templates == | ==== Classes as Object templates == | ||
<code lua> | <code lua> | ||
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</code> | </code> | ||
+ | ===== File access == | ||
+ | |||
+ | Each of the following constructs is equivalent, it reads a file line by line: | ||
+ | |||
+ | <code lua> | ||
+ | local f= io.open"file.txt" | ||
+ | repeat | ||
+ | local l= f:read("l") | ||
+ | if l then print(l) end | ||
+ | until not l | ||
+ | f:close() | ||
+ | </code> | ||
+ | |||
+ | <code lua> | ||
+ | local f= io.open"file.txt" | ||
+ | for l in f:lines("l") do | ||
+ | print(l) | ||
+ | end | ||
+ | f:close() | ||
+ | </code> | ||
+ | |||
+ | <code lua> | ||
+ | for l in io.lines("file.txt", "l") do | ||
+ | print(l) | ||
+ | end | ||
+ | </code> | ||
+ | |||
+ | - ''"l"'' as arg for ''read()'' is the default, it can be omitted | ||
+ | - ''file:lines()'' and ''io.lines()'' accept the same format args as ''read()''. (Tested. Nowhere found in docu). Thus you could read a file eg chunk by chunk as well. | ||
+ | - io.lines() without arguments returns an iterater wich returns stdin line by line | ||
+ | |||
+ | ==== Load CSV-like files == | ||
+ | |||
+ | <code lua> | ||
+ | #!/usr/bin/lua | ||
+ | local separator=":" | ||
+ | for line in io.lines() do | ||
+ | print(line) | ||
+ | for cell in line:gmatch("[^"..separator.."]+") do | ||
+ | print("", cell) | ||
+ | end | ||
+ | end | ||
+ | </code> | ||
===== Includes and Modules == | ===== Includes and Modules == | ||
==== Include == | ==== Include == |