Merge pull request #274 from Tieske/unpack

added an unpack that honors the n field

6 files changed, 44 insertions, 9 deletions

diff --git a/examples/symbols.lua b/examples/symbols.lua
index 1aed745..e73c4ba 100644
--- a/examples/symbols.lua
+++ b/examples/symbols.lua
@@ -4,7 +4,7 @@ local ops = require 'pl.operator'
 local List = require 'pl.List'
 local append,concat = table.insert,table.concat
 local compare,find_if,compare_no_order,imap,reduce,count_map = tablex.compare,tablex.find_if,tablex.compare_no_order,tablex.imap,tablex.reduce,tablex.count_map
-local unpack = utils.unpack
+local unpack = table.unpack
 
 function bindval (self,val)
     rawset(self,'value',val)
diff --git a/lua/pl/compat.lua b/lua/pl/compat.lua
index f3832b8..775e2cc 100644
--- a/lua/pl/compat.lua
+++ b/lua/pl/compat.lua
@@ -128,7 +128,6 @@ end
 --- pack an argument list into a table.
 -- @param ... any arguments
 -- @return a table with field n set to the length
--- @return the length
 -- @function table.pack
 if not table.pack then
     function table.pack (...)       -- luacheck: ignore
@@ -136,6 +135,15 @@ if not table.pack then
     end
 end
 
+--- unpack a table and return the elements.
+-- @param t table to unpack
+-- @param[opt] i index from which to start unpacking, defaults to 1
+-- @param[opt] t index of the last element to unpack, defaults to #t
+-- @return multiple returns values from the table
+if not table.unpack then
+    table.unpack = unpack           -- luacheck: ignore
+end
+
 ------
 -- return the full path where a Lua module name would be matched.
 -- @param mod module name, possibly dotted
diff --git a/lua/pl/func.lua b/lua/pl/func.lua
index f1f41f0..daac0fc 100644
--- a/lua/pl/func.lua
+++ b/lua/pl/func.lua
@@ -21,12 +21,11 @@ local type,setmetatable,getmetatable,rawset = type,setmetatable,getmetatable,raw
 local concat,append = table.concat,table.insert
 local tostring = tostring
 local utils = require 'pl.utils'
-local pairs,rawget,unpack = pairs,rawget,utils.unpack
+local pairs,rawget,unpack,pack = pairs,rawget,utils.unpack,utils.pack
 local tablex = require 'pl.tablex'
 local map = tablex.map
 local _DEBUG = rawget(_G,'_DEBUG')
 local assert_arg = utils.assert_arg
-local pack = table.pack or function(...) return { n = select("#", ...), ... } end
 
 local func = {}
 
diff --git a/lua/pl/test.lua b/lua/pl/test.lua
index ddf8345..2c3a5da 100644
--- a/lua/pl/test.lua
+++ b/lua/pl/test.lua
@@ -12,11 +12,10 @@ local tablex = require 'pl.tablex'
 local utils = require 'pl.utils'
 local pretty = require 'pl.pretty'
 local path = require 'pl.path'
-local type,unpack = type,utils.unpack
+local type,unpack,pack = type,utils.unpack,utils.pack
 local clock = os.clock
 local debug = require 'debug'
 local io = io
-local pack = table.pack or function(...) return { select("#", ...), ...} end
 
 local function dump(x)
     if type(x) == 'table' and not (getmetatable(x) and getmetatable(x).__tostring) then
diff --git a/lua/pl/utils.lua b/lua/pl/utils.lua
index bcd0e01..5b5a0d8 100644
--- a/lua/pl/utils.lua
+++ b/lua/pl/utils.lua
@@ -8,7 +8,7 @@ local format = string.format
 local compat = require 'pl.compat'
 local stdout = io.stdout
 local append = table.insert
-local unpack = rawget(_G,'unpack') or rawget(table,'unpack')
+local _unpack = table.unpack  -- always injected by 'compat'
 
 local utils = {
     _VERSION = "1.5.4",
@@ -19,9 +19,28 @@ local utils = {
     execute = compat.execute,
     dir_separator = compat.dir_separator,
     is_windows = compat.is_windows,
-    unpack = unpack
 }
 
+
+--- pack an argument list into a table.
+-- @param ... any arguments
+-- @return a table with field n set to the length
+-- @return table
+-- @function utils.pack
+utils.pack = table.pack  -- added here to be symmetrical with unpack
+
+--- unpack a table and return its contents.
+-- NOTE: this implementation differs from the Lua implementation in the way
+-- that this one DOES honor the n field in the table t, such that it is 'nil-safe'.
+-- @param t table to unpack
+-- @param[opt] i index from which to start unpacking, defaults to 1
+-- @param[opt] t index of the last element to unpack, defaults to `t.n` or #t
+-- @return multiple returns values from the table
+-- @function utils.unpack
+function utils.unpack(t, i, j)
+    return _unpack(t, i or 1, j or t.n or #t)
+end
+
 --- end this program gracefully.
 -- @param code The exit code or a message to be printed
 -- @param ... extra arguments for message's format'
@@ -209,7 +228,7 @@ end
 -- @usage first,next = splitv('jane:doe',':')
 -- @see split
 function utils.splitv (s,re)
-    return unpack(utils.split(s,re))
+    return _unpack(utils.split(s,re))
 end
 
 --- convert an array of values to strings.
diff --git a/tests/test-utils.lua b/tests/test-utils.lua
index b115bea..9ddc39d 100644
--- a/tests/test-utils.lua
+++ b/tests/test-utils.lua
@@ -123,6 +123,16 @@ asserteq(type(sin),"function")
 asserteq(type(abs),"function")
 
 
+-- packing and unpacking arguments in a nil-safe way
+local t = utils.pack(nil, nil, "hello", nil)
+asserteq(t.n, 4) -- the last nil does count as an argument
+
+local arg1, arg2, arg3, arg4 = utils.unpack(t)
+assert(arg1 == nil)
+assert(arg2 == nil)
+asserteq("hello", arg3)
+assert(arg4 == nil)
+