Recipes Lua - tsafin/tarantool GitHub Wiki
tarnatool> array = { 'Apple', 'Orange', 'Grapefruit', 'Banana'}
tarantool> for k, v in ipairs(array) do print(k, v) end
1 Apple
2 Orange
3 Grapefruit
4 Banana
---
...
tarantool> map = { k1 = 'v1', k2 = 'v2', k3 = 'v3' }
tarantool> for k, v in pairs(map) do print(k, v) end
k3 v3
k1 v1
k2 v2
---
...Remember: :func:`ipairs()` for arrays-like tables and :func:`pairs()` for map-like and mixed tables. :func:`ipairs()` is faster than :func:`pairs()`.
Use operator '#':
tarantool> array = { 1, 2, 3}
---
...
tarantool> #array
---
- 3
...Please note this operation has O(log(N)) complexity.
Try not to put nil in arrays. The length operator # will be confused and standard table functions like table.sort() will complain bitterly.
tarantool> t = {}
tarantool> t[1] = 1
tarantool> t[4] = 4
tarantool> t[10] = 10
tarantool> = #t --> NB!
---
- 1
...
tarantool> for k,v in pairs(t) do print(k,v) end
1 1
4 4
10 10Lua doens't store this value anywhere. Iterate over the table and calculate size:
tarantool> map = { a = 10, b = 15, c = 20 }
---
...
tarantool> size = 0; for _ in pairs(map) do size = size + 1; end
---
...
tarantool> size
---
- 3
...x, y = y, x-- define class objects
local myclass_somemethod = function(self)
print('test 1', self.data)
end
local myclass_someothermethod = function(self)
print('test 2', self.data)
end
local myclass_tostring = function(self)
return 'MyClass <'..self.data..'>'
end
local myclass_mt = {
__tostring = myclass_tostring;
__index = {
somemethod = myclass_somemethod;
someothermethod = myclass_someothermethod;
}
}
-- create a new object of myclass
local object = setmetatable({ data = 'data'}, myclass_mt)
print(object:somemethod())
print(object.data)See also:
collectgarbage('collect')See also :func:`collectgarbage` documentation.
Lua doesn't store nil in tables. a[2] = nil is semantically means
delete key 2 from a. However, you can store special NULL
value which is semantically identical to nil:
tarantool> json.encode({a = 10, b = nil, c = 20})
---
- '{"a":10,"c":20}'
...
tarantool> json.encode({a = 10, b = json.NULL, c = 20})
---
- '{"b":null,"a":10,"c":20}'
...
tarantool> json.NULL == nil
---
- true
...#!/usr/bin/env tarantool
local ffi = require('ffi')
ffi.cdef[[
int printf(const char *format, ...);
]]
ffi.C.printf("Hello, %s\n", os.getenv("USER"));See FFI tutorial for more examples.
#!/usr/bin/env tarantool
local ffi = require("ffi")
ffi.cdef[[
unsigned long compressBound(unsigned long sourceLen);
int compress2(uint8_t *dest, unsigned long *destLen,
const uint8_t *source, unsigned long sourceLen, int level);
int uncompress(uint8_t *dest, unsigned long *destLen,
const uint8_t *source, unsigned long sourceLen);
]]
local zlib = ffi.load(ffi.os == "Windows" and "zlib1" or "z")
-- Lua wrapper for compress2()
local function compress(txt)
local n = zlib.compressBound(#txt)
local buf = ffi.new("uint8_t[?]", n)
local buflen = ffi.new("unsigned long[1]", n)
local res = zlib.compress2(buf, buflen, txt, #txt, 9)
assert(res == 0)
return ffi.string(buf, buflen[0])
end
-- Lua wrapper for uncompress
local function uncompress(comp, n)
local buf = ffi.new("uint8_t[?]", n)
local buflen = ffi.new("unsigned long[1]", n)
local res = zlib.uncompress(buf, buflen, comp, #comp)
assert(res == 0)
return ffi.string(buf, buflen[0])
end
-- Simple test code.
local txt = string.rep("abcd", 1000)
print("Uncompressed size: ", #txt)
local c = compress(txt)
print("Compressed size: ", #c)
local txt2 = uncompress(c, #txt)
assert(txt2 == txt)See FFI tutorial for more examples.
local ffi = require("ffi")
ffi.cdef[[
typedef struct { double x, y; } point_t;
]]
local point
local mt = {
__add = function(a, b) return point(a.x+b.x, a.y+b.y) end,
__len = function(a) return math.sqrt(a.x*a.x + a.y*a.y) end,
__index = {
area = function(a) return a.x*a.x + a.y*a.y end,
},
}
point = ffi.metatype("point_t", mt)
local a = point(3, 4)
print(a.x, a.y) --> 3 4
print(#a) --> 5
print(a:area()) --> 25
local b = a + point(0.5, 8)
print(#b) --> 12.5Call :func:`gettimeofday()` or :func:`clock_gettime()` using Foreign Function Interface (FFI):
local ffi = require('ffi')
ffi.cdef[[
typedef long time_t;
typedef struct timeval {
time_t tv_sec;
time_t tv_usec;
} timeval;
int gettimeofday(struct timeval *t, void *tzp);
]]
-- Function for getting current time
local timeval_buf = ffi.new("timeval")
local now = function()
ffi.C.gettimeofday(timeval_buf, nil)
return tonumber(timeval_buf.tv_sec * 1000 + (timeval_buf.tv_usec / 1000))
end