Lua (5.3) Language addition (#4804)

* starting Lua port of python implmention. Syncing commit

* Bulk of Lua module port from Python done. Not tested, only static analysis. Need to work on binary strings. Started work on flatc lua code generation

* Fixed all the basic errors to produced a binary output from the builder, don't know if it is generated correctly, but it contains data, so that must be good

* fixed binary set command that was extending the array improperly

* continued improvement

* Moved lua submodules down a directory so their names don't clash with potential other modules. Added compat module to provide Lua versioning logic

* Successful sample port from Python

* working on testing Lua code with formal tests

* continued to work on tests and fixes to code to make tests pass

* Added reading buffer test

* Changed binaryarray implmentation to use a temporary table for storing data, and then serialize it to a string when requested. This double the rate of building flatbuffers compared to the string approach.

* Didn't need encode module as it just added another layer of indirection that isn't need

* profiled reading buffers, optimizations to increase read performance of monster data to ~7 monster / millisecond

* Writing profiler improvments. Get about
~2 monsters/millisecond building rate

* removed Numpy generation from Lua (came from the Python port)

* math.pow is deprecated in Lua 5.3, so changed to ^ notation. Also added .bat script for starting Lua tests

* adding results of generate_code.bat

* simple edits for code review in PR.

* There was a buffer overflow in inserting the keywords into the unorder set for both the Lua and Python code gens. Changed insertion to use iterators.

* fixed spacing issue

* basic documenation/tutorial updates. Updated sample_binary.lua to reflect the tutorial better

* removed windows-specific build step in Lua tests

lua/flatbuffers.lua

@@ -0,0 +1,8 @@
+local m = {}
+
+m.Builder = require("flatbuffers.builder").New
+m.N = require("flatbuffers.numTypes")
+m.view = require("flatbuffers.view")
+m.binaryArray = require("flatbuffers.binaryarray")
+
+return m

lua/flatbuffers/binaryarray.lua

@@ -0,0 +1,123 @@
+local m = {} -- the module table
+
+local mt = {} -- the module metatable
+
+-- given a binary array, set a metamethod to return its length
+-- (e.g., #binaryArray, calls this)
+function mt:__len()
+    return self.size
+end
+
+-- Create a new binary array of an initial size
+function m.New(sizeOrString)
+    -- the array storage itself
+    local o = {}
+    
+    if type(sizeOrString) == "string" then
+        o.str = sizeOrString
+        o.size = #sizeOrString
+    elseif type(sizeOrString) == "number" then
+        o.data = {}
+        o.size = sizeOrString
+    else
+        error("Expect a integer size value or string to construct a binary array")
+    end
+    -- set the inheritance
+    setmetatable(o, {__index = mt, __len = mt.__len})
+    return o
+end
+
+-- Get a slice of the binary array from start to end position
+function mt:Slice(startPos, endPos)
+    startPos = startPos or 0
+    endPos = endPos or self.size
+    local d = self.data
+    if d then
+        -- if the self.data is defined, we are building the buffer
+        -- in a Lua table
+        
+        -- new table to store the slice components
+        local b = {}
+        
+        -- starting with the startPos, put all
+        -- values into the new table to be concat later
+        -- updated the startPos based on the size of the
+        -- value
+        while startPos < endPos do
+            local v = d[startPos] or '/0'
+            table.insert(b, v)
+            startPos = startPos + #v
+        end
+
+        -- combine the table of strings into one string
+        -- this is faster than doing a bunch of concats by themselves
+        return table.concat(b)
+    else
+        -- n.b start/endPos are 0-based incoming, so need to convert
+        --     correctly. in python a slice includes start -> end - 1
+        return self.str:sub(startPos+1, endPos)
+    end
+end
+
+-- Grow the binary array to a new size, placing the exisiting data
+-- at then end of the new array
+function mt:Grow(newsize)
+    -- the new table to store the data
+    local newT = {}
+    
+    -- the offset to be applied to existing entries
+    local offset = newsize - self.size
+    
+    -- loop over all the current entries and
+    -- add them to the new table at the correct
+    -- offset location
+    local d = self.data
+    for i,data in pairs(d) do
+        newT[i + offset] = data
+    end
+    
+    -- update this storage with the new table and size
+    self.data = newT
+    self.size = newsize
+end
+
+-- memorization for padding strings
+local pads = {}
+
+-- pad the binary with n \0 bytes at the starting position
+function mt:Pad(n, startPos)
+    -- use memorization to avoid creating a bunch of strings
+    -- all the time
+    local s = pads[n]
+    if not s then
+        s = string.rep('\0', n)
+        pads[n] = s
+    end
+    
+    -- store the padding string at the start position in the
+    -- Lua table
+    self.data[startPos] = s
+end
+
+-- Sets the binary array value at the specified position
+function mt:Set(value, position)
+    self.data[position] = value
+end
+
+-- locals for slightly faster access
+local sunpack = string.unpack
+local spack = string.pack
+
+-- Pack the data into a binary representation
+function m.Pack(fmt, ...)
+    return spack(fmt, ...)
+end
+
+-- Unpack the data from a binary representation in
+-- a Lua value
+function m.Unpack(fmt, s, pos)
+    return sunpack(fmt, s.str, pos + 1)
+end
+
+-- Return the binary array module
+return m

lua/flatbuffers/builder.lua

@@ -0,0 +1,368 @@
+local N = require("flatbuffers.numTypes")
+local ba = require("flatbuffers.binaryarray")
+local compat = require("flatbuffers.compat")
+
+local m = {}
+
+local mt = {}
+
+-- get locals for faster access
+local VOffsetT  = N.VOffsetT
+local UOffsetT  = N.UOffsetT
+local SOffsetT  = N.SOffsetT
+local Bool      = N.Bool
+local Uint8     = N.Uint8
+local Uint16    = N.Uint16
+local Uint32    = N.Uint32
+local Uint64    = N.Uint64
+local Int8      = N.Int8
+local Int16     = N.Int16
+local Int32     = N.Int32
+local Int64     = N.Int64
+local Float32   = N.Float32
+local Float64   = N.Float64
+
+local MAX_BUFFER_SIZE = 0x80000000 -- 2 GB
+local VtableMetadataFields = 2
+
+local getAlignSize = compat.GetAlignSize
+
+local function vtableEqual(a, objectStart, b)
+    UOffsetT:EnforceNumber(objectStart)
+    if (#a * VOffsetT.bytewidth) ~= #b then
+        return false
+    end
+    
+    for i, elem in ipairs(a) do
+        local x = VOffsetT:Unpack(b, i * VOffsetT.bytewidth)
+        if x ~= 0 or elem ~= 0 then
+            local y = objectStart - elem
+            if x ~= y then
+                return false
+            end
+        end
+    end
+    return true
+end
+
+function m.New(initialSize)
+    assert(0 <= initialSize and initialSize < MAX_BUFFER_SIZE)
+    local o = 
+    {
+        finished = false,
+        bytes = ba.New(initialSize),
+        nested = false,
+        head = initialSize,
+        minalign = 1,
+        vtables = {}
+    }
+    setmetatable(o, {__index = mt})
+    return o
+end
+
+function mt:Output(full)
+    assert(self.finished, "Builder Not Finished")
+    if full then
+        return self.bytes:Slice()
+    else
+        return self.bytes:Slice(self.head)
+    end
+end
+
+function mt:StartObject(numFields)
+    assert(not self.nested)
+    
+    local vtable = {}
+
+    for _=1,numFields do
+        table.insert(vtable, 0)
+    end
+            
+    self.currentVTable = vtable
+    self.objectEnd = self:Offset()
+    self.minalign = 1
+    self.nested = true
+end
+
+function mt:WriteVtable()
+    self:PrependSOffsetTRelative(0)
+    local objectOffset = self:Offset()
+    
+    local exisitingVTable
+    local i = #self.vtables
+    while i >= 1 do
+        if self.vtables[i] == 0 then
+            table.remove(self.vtables,i)
+        end
+        i = i - 1
+    end    
+   
+    while i >= 1 do
+        
+        local vt2Offset = self.vtables[i]
+        local vt2Start = #self.bytes - vt2Offset
+        local vt2len = VOffsetT:Unpack(self.bytes, vt2Start)
+        
+        local metadata = VtableMetadataFields * VOffsetT.bytewidth
+        local vt2End = vt2Start + vt2Len
+        local vt2 = self.bytes:Slice(vt2Start+metadata,vt2End)
+        
+        if vtableEqual(self.currentVTable, objectOffset, vt2) then
+            exisitingVTable = vt2Offset
+            break
+        end
+        
+        i = i - 1
+    end
+    
+    if not exisitingVTable then
+        i = #self.currentVTable
+        while i >= 1 do
+            local off = 0
+            local a = self.currentVTable[i]
+            if a and a ~= 0 then
+                off = objectOffset - a
+            end
+            self:PrependVOffsetT(off)
+            
+            i = i - 1
+        end
+        
+        local objectSize = objectOffset - self.objectEnd
+        self:PrependVOffsetT(objectSize)
+        
+        local vBytes = #self.currentVTable + VtableMetadataFields
+        vBytes = vBytes * VOffsetT.bytewidth
+        self:PrependVOffsetT(vBytes)
+        
+        local objectStart = #self.bytes - objectOffset
+        self.bytes:Set(SOffsetT:Pack(self:Offset() - objectOffset),objectStart)        
+        
+        table.insert(self.vtables, self:Offset())
+    else
+        local objectStart = #self.bytes - objectOffset
+        self.head = objectStart
+        self.bytes:Set(SOffsetT:Pack(exisitingVTable - objectOffset),self.head)
+    end
+    
+    self.currentVTable = nil
+    return objectOffset
+end
+
+function mt:EndObject()
+    assert(self.nested)
+    self.nested = false
+    return self:WriteVtable()
+end
+
+local function growByteBuffer(self, desiredSize)
+    local s = #self.bytes
+    assert(s < MAX_BUFFER_SIZE, "Flat Buffers cannot grow buffer beyond 2 gigabytes")
+    local newsize = s
+    repeat
+        newsize = math.min(newsize * 2, MAX_BUFFER_SIZE)
+        if newsize == 0 then newsize = 1 end
+    until newsize > desiredSize 
+    
+    self.bytes:Grow(newsize)
+end
+
+function mt:Head()
+    return self.head
+end
+
+function mt:Offset()
+   return #self.bytes - self.head
+end
+
+function mt:Pad(n)    
+    if n > 0 then
+        -- pads are 8-bit, so skip the bytewidth lookup
+        local h = self.head - n  -- UInt8    
+        self.head = h
+        self.bytes:Pad(n, h)  
+    end
+end
+
+function mt:Prep(size, additionalBytes)
+    if size > self.minalign then
+        self.minalign = size
+    end
+
+    local h = self.head
+    
+    local k = #self.bytes - h + additionalBytes
+    local alignsize = ((~k) + 1) & (size - 1) -- getAlignSize(k, size)
+
+    local desiredSize = alignsize + size + additionalBytes
+
+    while self.head < desiredSize do
+        local oldBufSize = #self.bytes
+        growByteBuffer(self, desiredSize)
+        local updatedHead = self.head + #self.bytes - oldBufSize
+        self.head = updatedHead
+    end
+    
+    self:Pad(alignsize)
+end
+
+function mt:PrependSOffsetTRelative(off)
+    self:Prep(SOffsetT.bytewidth, 0)
+    assert(off <= self:Offset(), "Offset arithmetic error")
+    local off2 = self:Offset() - off + SOffsetT.bytewidth
+    self:Place(off2, SOffsetT)
+end
+
+function mt:PrependUOffsetTRelative(off)
+    self:Prep(UOffsetT.bytewidth, 0)
+    local soffset = self:Offset()
+    if off <= soffset then    
+        local off2 = soffset - off + UOffsetT.bytewidth
+        self:Place(off2, UOffsetT)
+    else
+        error("Offset arithmetic error")
+    end
+end
+
+function mt:StartVector(elemSize, numElements, alignment)
+    assert(not self.nested)
+    self.nested = true
+    self:Prep(Uint32.bytewidth, elemSize * numElements)
+    self:Prep(alignment, elemSize * numElements)
+    return self:Offset()
+end
+
+function mt:EndVector(vectorNumElements)
+    assert(self.nested)
+    self.nested = false
+    self:Place(vectorNumElements, UOffsetT)    
+    return self:Offset()
+end
+
+function mt:CreateString(s)
+    assert(not self.nested)
+    self.nested = true
+    
+    assert(type(s) == "string")
+    
+    self:Prep(UOffsetT.bytewidth, (#s + 1)*Uint8.bytewidth)
+    self:Place(0, Uint8)
+    
+    local l = #s
+    self.head = self.head - l
+    
+    self.bytes:Set(s, self.head, self.head + l)
+    
+    return self:EndVector(#s)
+end
+
+function mt:CreateByteVector(x)
+    assert(not self.nested)
+    self.nested = true
+    self:Prep(UOffsetT.bytewidth, #x*Uint8.bytewidth)
+    
+    local l = #x
+    self.head = self.head - l
+    
+    self.bytes:Set(x, self.head, self.head + l)
+    
+    return self:EndVector(#x)
+end
+
+function mt:Slot(slotnum)
+    assert(self.nested)
+    -- n.b. slot number is 0-based
+    self.currentVTable[slotnum + 1] = self:Offset()
+end
+
+local function finish(self, rootTable, sizePrefix)
+    UOffsetT:EnforceNumber(rootTable)
+    local prepSize = UOffsetT.bytewidth
+    if sizePrefix then
+        prepSize = prepSize + Int32.bytewidth
+    end
+    
+    self:Prep(self.minalign, prepSize)
+    self:PrependUOffsetTRelative(rootTable)
+    if sizePrefix then
+        local size = #self.bytes - self.head
+        Int32:EnforceNumber(size)
+        self:PrependInt32(size)
+    end
+    self.finished = true
+    return self.head
+end
+
+function mt:Finish(rootTable)
+    return finish(self, rootTable, false)
+end
+
+function mt:FinishSizePrefixed(rootTable)
+    return finish(self, rootTable, true)
+end
+
+function mt:Prepend(flags, off)
+    self:Prep(flags.bytewidth, 0)
+    self:Place(off, flags)
+end
+
+function mt:PrependSlot(flags, o, x, d)
+    flags:EnforceNumber(x)
+    flags:EnforceNumber(d)
+    if x ~= d then
+        self:Prepend(flags, x)
+        self:Slot(o)
+    end
+end
+
+function mt:PrependBoolSlot(...)    self:PrependSlot(Bool, ...) end
+function mt:PrependByteSlot(...)    self:PrependSlot(Uint8, ...) end
+function mt:PrependUint8Slot(...)   self:PrependSlot(Uint8, ...) end
+function mt:PrependUint16Slot(...)  self:PrependSlot(Uint16, ...) end
+function mt:PrependUint32Slot(...)  self:PrependSlot(Uint32, ...) end
+function mt:PrependUint64Slot(...)  self:PrependSlot(Uint64, ...) end
+function mt:PrependInt8Slot(...)    self:PrependSlot(Int8, ...) end
+function mt:PrependInt16Slot(...)   self:PrependSlot(Int16, ...) end
+function mt:PrependInt32Slot(...)   self:PrependSlot(Int32, ...) end
+function mt:PrependInt64Slot(...)   self:PrependSlot(Int64, ...) end
+function mt:PrependFloat32Slot(...) self:PrependSlot(Float32, ...) end
+function mt:PrependFloat64Slot(...) self:PrependSlot(Float64, ...) end
+
+function mt:PrependUOffsetTRelativeSlot(o,x,d)
+    if x~=d then
+        self:PrependUOffsetTRelative(x)
+        self:Slot(o)
+    end
+end
+
+function mt:PrependStructSlot(v,x,d)
+    UOffsetT:EnforceNumber(d)
+    if x~=d then
+        UOffsetT:EnforceNumber(x)
+        assert(x == self:Offset(), "Tried to write a Struct at an Offset that is different from the current Offset of the Builder.")
+        self:Slot(v)
+    end
+end
+
+function mt:PrependBool(x)      self:Prepend(Bool, x) end
+function mt:PrependByte(x)      self:Prepend(Uint8, x) end
+function mt:PrependUint8(x)     self:Prepend(Uint8, x) end
+function mt:PrependUint16(x)    self:Prepend(Uint16, x) end
+function mt:PrependUint32(x)    self:Prepend(Uint32, x) end
+function mt:PrependUint64(x)    self:Prepend(Uint64, x) end
+function mt:PrependInt8(x)      self:Prepend(Int8, x) end
+function mt:PrependInt16(x)     self:Prepend(Int16, x) end
+function mt:PrependInt32(x)     self:Prepend(Int32, x) end
+function mt:PrependInt64(x)     self:Prepend(Int64, x) end
+function mt:PrependFloat32(x)   self:Prepend(Float32, x) end
+function mt:PrependFloat64(x)   self:Prepend(Float64, x) end
+function mt:PrependVOffsetT(x)  self:Prepend(VOffsetT, x) end
+
+function mt:Place(x, flags)
+    local d = flags:EnforceNumberAndPack(x)
+    local h = self.head - flags.bytewidth
+    self.head = h
+    self.bytes:Set(d, h)
+end
+
+return m

lua/flatbuffers/compat.lua

@@ -0,0 +1,17 @@
+local m = {}
+
+local getAlignSize
+if _VERSION == "Lua 5.3" then
+    getAlignSize = function(k, size)
+            return ((~k) + 1) & (size - 1)
+        end    
+else
+    getAlignSize = function(self, size, additionalBytes)        
+        local alignsize = bit32.bnot(#self.bytes-self:Head() + additionalBytes) + 1
+        return bit32.band(alignsize,(size - 1))
+    end
+end
+    
+m.GetAlignSize = getAlignSize
+
+return m

lua/flatbuffers/numTypes.lua

@@ -0,0 +1,198 @@
+local m = {}
+
+local ba = require("flatbuffers.binaryarray")
+
+local bpack = ba.Pack
+local bunpack = ba.Unpack
+
+local type_mt =  {}
+
+function type_mt:Pack(value)
+    return bpack(self.packFmt, value)
+end
+
+function type_mt:Unpack(buf, pos)    
+    return bunpack(self.packFmt, buf, pos)
+end
+
+function type_mt:ValidNumber(n)
+    if not self.min_value and not self.max_value then return true end
+    return self.min_value <= n and n <= self.max_value
+end
+
+function type_mt:EnforceNumber(n)
+    -- duplicate code since the overhead of function calls 
+    -- for such a popular method is time consuming
+    if not self.min_value and not self.max_value then 
+        return 
+    end
+    
+    if self.min_value <= n and n <= self.max_value then 
+        return
+    end    
+    
+    error("Number is not in the valid range") 
+end
+
+function type_mt:EnforceNumberAndPack(n)
+    return bpack(self.packFmt, n)    
+end
+
+function type_mt:ConvertType(n, otherType)
+    assert(self.bytewidth == otherType.bytewidth, "Cannot convert between types of different widths")
+    if self == otherType then
+        return n
+    end
+    return otherType:Unpack(self:Pack(n))
+end
+
+local bool_mt =
+{
+    bytewidth = 1,
+    min_value = false,
+    max_value = true,
+    lua_type = type(true),
+    name = "bool",
+    packFmt = "<b"
+}
+
+local uint8_mt = 
+{
+    bytewidth = 1,
+    min_value = 0,
+    max_value = 2^8-1,
+    lua_type = type(1),
+    name = "uint8",
+    packFmt = "<I1"
+}
+
+local uint16_mt = 
+{
+    bytewidth = 2,
+    min_value = 0,
+    max_value = 2^16-1,
+    lua_type = type(1),
+    name = "uint16",
+    packFmt = "<I2"
+}
+
+local uint32_mt = 
+{
+    bytewidth = 4,
+    min_value = 0,
+    max_value = 2^32-1,
+    lua_type = type(1),
+    name = "uint32",
+    packFmt = "<I4"
+}
+
+local uint64_mt = 
+{
+    bytewidth = 8,
+    min_value = 0,
+    max_value = 2^64-1,
+    lua_type = type(1),
+    name = "uint64",
+    packFmt = "<I8"
+}
+
+local int8_mt = 
+{
+    bytewidth = 1,
+    min_value = -2^7,
+    max_value = 2^7-1,
+    lua_type = type(1),
+    name = "int8",
+    packFmt = "<i1"
+}
+
+local int16_mt = 
+{
+    bytewidth = 2,
+    min_value = -2^15,
+    max_value = 2^15-1,
+    lua_type = type(1),
+    name = "int16",
+    packFmt = "<i2"
+}
+
+local int32_mt = 
+{
+    bytewidth = 4,
+    min_value = -2^15,
+    max_value = 2^15-1,
+    lua_type = type(1),
+    name = "int32",
+    packFmt = "<i4"
+}
+
+local int64_mt = 
+{
+    bytewidth = 8,
+    min_value = -2^63,
+    max_value = 2^63-1,
+    lua_type = type(1),
+    name = "int64",
+    packFmt = "<i8"
+}
+
+local float32_mt = 
+{
+    bytewidth = 4,
+    min_value = nil,
+    max_value = nil,
+    lua_type = type(1.0),
+    name = "float32",
+    packFmt = "<f"
+}
+
+local float64_mt = 
+{
+    bytewidth = 8,
+    min_value = nil,
+    max_value = nil,
+    lua_type = type(1.0),
+    name = "float64",
+    packFmt = "<d"
+}
+
+-- register the base class
+setmetatable(bool_mt, {__index = type_mt})
+setmetatable(uint8_mt, {__index = type_mt})
+setmetatable(uint16_mt, {__index = type_mt})
+setmetatable(uint32_mt, {__index = type_mt})
+setmetatable(uint64_mt, {__index = type_mt})
+setmetatable(int8_mt, {__index = type_mt})
+setmetatable(int16_mt, {__index = type_mt})
+setmetatable(int32_mt, {__index = type_mt})
+setmetatable(int64_mt, {__index = type_mt})
+setmetatable(float32_mt, {__index = type_mt})
+setmetatable(float64_mt, {__index = type_mt})
+
+
+m.Bool      = bool_mt
+m.Uint8     = uint8_mt
+m.Uint16    = uint16_mt
+m.Uint32    = uint32_mt
+m.Uint64    = uint64_mt
+m.Int8      = int8_mt
+m.Int16     = int16_mt
+m.Int32     = int32_mt
+m.Int64     = int64_mt
+m.Float32   = float32_mt
+m.Float64   = float64_mt
+
+m.UOffsetT  = uint32_mt
+m.VOffsetT  = uint16_mt
+m.SOffsetT  = int32_mt
+
+function GenerateTypes(listOfTypes)
+    for _,t in pairs(listOfTypes) do
+        t.Pack = function(self, value) return bpack(self.packFmt, value) end
+        t.Unpack = function(self, buf, pos) return bunpack(self.packFmt, buf, pos) end
+    end
+end
+
+GenerateTypes(m)
+
+return m

lua/flatbuffers/view.lua

@@ -0,0 +1,97 @@
+local m = {}
+local mt = {}
+
+local mt_name = "flatbuffers.view.mt"
+
+local N = require("flatbuffers.numTypes")
+local binaryarray = require("flatbuffers.binaryarray")
+
+function m.New(buf, pos)
+    N.UOffsetT:EnforceNumber(pos)
+    
+    -- need to convert from a string buffer into
+    -- a binary array
+
+    local o = {
+        bytes = type(buf) == "string" and binaryarray.New(buf) or buf,
+        pos = pos
+    }
+    setmetatable(o, {__index = mt, __metatable = mt_name})
+    return o
+end
+
+function mt:Offset(vtableOffset)
+    local vtable = self.pos - self:Get(N.SOffsetT, self.pos)
+    local vtableEnd = self:Get(N.VOffsetT, vtable)
+    if vtableOffset < vtableEnd then
+        return self:Get(N.VOffsetT, vtable + vtableOffset)
+    end
+    return 0
+end
+
+function mt:Indirect(off)
+    N.UOffsetT:EnforceNumber(off)
+    return off + N.UOffsetT:Unpack(self.bytes, off)
+end
+
+function mt:String(off)
+    N.UOffsetT:EnforceNumber(off)
+    off = off + N.UOffsetT:Unpack(self.bytes, off)
+    local start = off + N.UOffsetT.bytewidth
+    local length = N.UOffsetT:Unpack(self.bytes, off)
+    return self.bytes:Slice(start, start+length)
+end
+
+function mt:VectorLen(off)
+    N.UOffsetT:EnforceNumber(off)
+    off = off + self.pos
+    off = off + N.UOffsetT:Unpack(self.bytes, off)
+    return N.UOffsetT:Unpack(self.bytes, off)
+end
+
+function mt:Vector(off)
+    N.UOffsetT:EnforceNumber(off)
+    
+    off = off + self.pos
+    local x = off + self:Get(N.UOffsetT, off)
+    x = x + N.UOffsetT.bytewidth
+    return x
+end
+
+function mt:Union(t2, off)
+    assert(getmetatable(t2) == mt_name)
+    N.UOffsetT:EnforceNumber(off)
+    
+    off = off + self.pos
+    t2.pos = off + self:Get(N.UOffsetT, off)
+    t2.bytes = self.bytes
+end
+
+function mt:Get(flags, off)
+    N.UOffsetT:EnforceNumber(off)
+    return flags:Unpack(self.bytes, off)
+end
+
+function mt:GetSlot(slot, d, validatorFlags)
+    N.VOffsetT:EnforceNumber(slot)
+    if validatorFlags then
+        validatorFlags:EnforceNumber(d)
+    end
+    local off = self:Offset(slot)
+    if off == 0 then
+        return d
+    end
+    return self:Get(validatorFlags, self.pos + off)
+end
+
+function mt:GetVOffsetTSlot(slot, d)
+    N.VOffsetT:EnforceNumber(slot)
+    N.VOffsetT:EnforceNumber(d)
+    local off = self:Offset(slot)
+    if off == 0 then
+        return d
+    end
+    return off
+end
+
+return m