how do you think of supporting closure serialization of lua?

[yuin]

how do you think of supporting closure serialization of lua?

[yuin]

Closure serialization in GopherLua is quite hard to make it possible for some reasones.

1. GopherLua is based on Lua5.1 : Closures in Lua5.1 refers the global environment. (Lua5.2 or newer has no global environment. The global environment is expressed as an upvalue.).
2. GopherLua does not have bytecode dump functionality : Byte codes in Gopher are just intermediate representation.

If it is must, I'd probably try that like this:

1. Assumptions1 : Ａ local and remote VM share the same global variables.
2. Assumptions2 : Closures do not have a metatable.
3. Assumptions3 : Closures do not refer any upvalues.
4. Dump an LFunction object into a byte array by encoding/gob ( LFunctionProto has private members, so you will have to reflections) .
5. Load the byte array and set clo.Env = (remote global LTable) .

[xtaci]

Yes, It's hard, but it's quite useful.

Instead of distributing data, we can distribute procedures, It is much more useful than data only parallel.
All Assumptions are acceptable at this stage I think.
I really hope this feature can be added to gopher-lua.

(Assumption3. Upvalue capturing is hard, I think AST will help.)

[yuin]

If it is possible to implement as a library, that should not be included GopherLua because GopherLua is Lua. Lua's philosophy is to keep itself as small as possible, but to provide functionalities that make it possible to add major language features as needed.

If you need to some functionalities to implement it, I will examine new functionalities that help you.

[xtaci]

Steps:

1. implement function string.dump bytecode (gob maybe)
2. getupvalues for functions
3. (other side) setupvalues & loadstring

How do you think of this ?

[yuin]

You had better stop handling upvalues.

In original Lua5.1, functions with upvalues can be dumped by string.dump, but all upvalues are initialized with nil and not shared with any other functions.
In addition, in original Lua5.0, functions with upvalues can NOT be dumped by string.dump (causes an error).

These facts underline the difficulty of handling upvalues in this job.

[xtaci]

so you still suggest manually SetGlobal(variables) & DoString(function f()) ?

[yuin]

Yes, It is simplest way.
Or, write serializer for the FunctionProto struct using some reflections(yes, nearly equals to string.dump) and construct an LFunction object without upvalues(or with nil initialized upvalues).

encoding/gob will not be suitable for writing a serializer for the FunctionProto struct because it has some unexported fields.

[xtaci]

this is a sample for how I use it. A name change procedure to be executed in remote.

[shabbyrobe]

I have a very similar use case to this. I was thinking I could mark certain functions that I care about and extract the code from the AST, but that doesn't look possible either because the AST only contains line numbers, not token positions. Am I missing something? If not, would you accept a PR that puts the token positions into the AST?