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+--- Alpine Configurator utility functions.
+--
+-- @module aconf.util
+
+--[[
+Copyright (c) 2012-2014 Kaarle Ritvanen
+See LICENSE file for license details
+--]]
+
+
+local M = {}
+
+--- set default value for a key in a table unless it is already set.
+-- @param t the table
+-- @param k the key
+-- @param v the default value
+-- @return the value `t[k]`
+function M.setdefault(t, k, v)
+ if t[k] == nil then t[k] = v end
+ return t[k]
+end
+
+--- merge a table into another.
+-- Copy values for all keys from `src` to `dst` and optionally keep existing
+-- values.
+-- @param dst the destination table
+-- @param src the source table
+-- @param preserve a boolean. If true then will existing entries in `dst` be
+-- kept.
+-- @return the destination table, `dst`
+function M.update(dst, src, preserve)
+ for k, v in pairs(src) do
+ if not preserve or dst[k] == nil then dst[k] = v end
+ end
+ return dst
+end
+
+--- copy default vaules from one table to another.
+-- Copy all entries in `src` to `dst` but keep any already existing values
+-- in `dst`.
+-- @param dst the destination table
+-- @param src the source table containing the default values
+-- @return the destination table, `dst`
+function M.setdefaults(dst, src) return M.update(dst, src, true) end
+
+--- copy a varable.
+-- If `var` is a table, then the table is cloned, otherwise return the value
+-- of `var`.
+-- @param var the variable to copy
+-- @return a clone of `var`
+function M.copy(var)
+ return type(var) == 'table' and M.setdefaults({}, var) or var
+end
+
+--- extend an array.
+-- inserts all elements in `src` into `dst`
+-- @param dst the destination array
+-- @param src the source array
+-- @return the destination array, `dst`
+function M.extend(dst, src)
+ for _, v in ipairs(src) do table.insert(dst, v) end
+ return dst
+end
+
+--- extract the keys of a table as an array.
+-- @param tbl a table
+-- @return an array of keys
+function M.keys(tbl)
+ local res = {}
+ for k, v in pairs(tbl) do table.insert(res, k) end
+ return res
+end
+
+--- determine whether a value is present in an array.
+-- @param list an array
+-- @param value a value
+-- @return a boolean
+function M.contains(list, value)
+ for k, v in ipairs(list) do if v == value then return true end end
+ return false
+end
+
+--- map a function over a table.
+-- @param func a function with one argument
+-- @param tbl the table
+-- @return the transformed table
+function M.map(func, tbl)
+ local res = {}
+ for k, v in pairs(tbl) do res[k] = func(v) end
+ return res
+end
+
+--- select array values satisfying a filter.
+-- @param func a function with one argument
+-- @param list the array
+-- @return the filtered array
+function M.filter(func, list)
+ local res = {}
+ for _, v in ipairs(list) do if func(v) then table.insert(res, v) end end
+ return res
+end
+
+return M