transforms(变换)库提供了一套用于带索引表的实用工具。此运行库提供了高度可复用的特殊迭代器，这些迭代器是 text 与 sh 命令解析的核心。
所有的transform方法都预期在序列上迭代，参见https://www.lua.org/manual/5.2/manual.html#3.4.6
此API所有的 first 与 last 参数均与string方法（例如string.sub）中的 first 与 last 参数工作方式一致。因此可以接收负值，负值为从后向前数。first（当选择时）默认相当于 1，而 last 默认相当于 -1。
predicate(element: value, index: number, tbl: table): number, number
此判断函数会在 tbl的每个索引上依次调用。 element 为 tbl[index] 中的值。通常而言，判断函数将会忽略 index 与 tbl，仅处理element。但一些判断函数可能会需要检查tbl中在index之前或之后的值。（重要！）应注意，传递给判断函数的tbl实际上只是传递给transform api的原始表的一个视图（view）。此处的视图（view）不是原生的序列，而是只会返回tbl中 [first, last] 范围内的值。
换言之，判断函数处理一个“元素组”，并返回代表满足的条件的值。
* 元素组
“元素组”一词代指下列之一：
A)传递给判断函数的单个element。与tbl[index]的值为同一个。
或者
B)tbl中自index起的元素序列。判断函数可能会从index处开始迭代，数量为其需要检查的元素数，直到 #tbl 为止。
* 返回值
返回值的可能情况：
false 或 nil，代表元素组不满足判断函数的条件。
index，代表满足条件。函数应当直接返回给定函数的索引号，也就是元素组的起始元素索引号。
nil。
transforms.first()。
一些transform方法可能会指定其他可用的判断数据类型，例如表或字符串。这些判断函数的用法特定于对应的方法，且在此处详细列出的方法中定义。
==== Methods ====
* transforms.sub(tbl: table, first: number, last: number or nil): table
Behaves similarly to string.sub. Returns a sub table of tbl from first to last.
* transforms.first(tbl: table, predicate: function or table, first: number or nil, last: number or nil): number, number
Returns the first index in tbl (between indexes first and last, inclusively) where predicate is satisfied. The 2nd return is also the ending index of the match. General examples will have the same two values returned, i.e. a match of length 1. The predicate can (optionally) return a 2nd return value to indicate the size of the match.
In the case that predicate is a table, transforms.first() returns the starting and ending index of the first matching sub table in tbl that matches ANY one of the tables in predicate.
Examples:
lua
local tx = require("transforms")
print( tx.first ( { 1, 1, 3, 2, 4, 7 }, function(e, i, tbl)
local evens = 0
for i=i,#tbl do
if tbl[i] % 2 == 0 then
evens = evens + 1
else
break
end
end
return evens > 0, evens
end))
Output
4 5
lua
local tx = require("transforms")
print( tx.first ( { 1, 1, 3, 2, 4, 7 }, { {1, 2}, {3, 2, 4} }) )
Output
3 5
* transforms.partition(tbl: table, partioner: function, first: number or nil, last: number or nil): table of tables
Returns a list of sub lists from tbl, generated by partioner within the range from first to last. partioner is a predicate function, defined above.
The index parameter passed to the partitioner will skip ranges, i.e. it will increase by n where n is the size of the partition.
The partitioner predicate for this method must return the starting AND ending index of satisfied element sets. Again, see the predicate info above.
* transforms.begins(tbl: table, sub: table, first: number or nil, last: number or nil)
Returns true if the subset of tbl from first to last fully composes v aligned at the first index. Assuming first and last have been adjusted for negative wrap around, that is to say:
v[1] == tbl[first + 0]
v[2] == tbl[first + 1]
…
v[#v] == tbl[first + #v - 1]
Where first + #v - 1 is within the bounds of [first, last] of tbl.
* transforms.foreach(tbl: table, adapter: function, first: number or nil, last: number or nil)
Returns an adaptation of each element in tbl from first to last. Any nil result of the adapter is ignored, and not appended to the result.
adapter follows the predicate signature except for the handling of the return values
* Adapter Returns
The simple case is to return a single value. E.g. tx.foreach({'a', 'b', 'c'}, string.upper) would return {'A', 'B', 'C'}.
nil to skip a value. E.g. tx.foreach({'1', 'foobar', '2'}, function(n) return tonumber(n) end) would return {1, 2}.
But the adapter can return a second value that is used in place of the next sequence number. E.g. tx.foreach({'1','foobar','3'},function(n,i) return tonumber(n), tostring(i) end) would return {["1"]=1, ["3"]=3}
目录
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