Dynamically generating a module fails on master (sometimes on 0.2)

[bfredl]

I'm experimenting a bit with auto-generating bindings to Gtk3/Clutter/etc using GObject-introspection in a fork of Gtk.jl (https://github.com/bfredl/Gtk.jl )

My current approach depends on dynamically generating modules and I'm using

module GI
    function create_module(modname::Symbol)
        eval(quote module ($modname) end; $modname end)
    end
    setconst(mod,name,val) = eval(mod, :(const $name = $(Expr(:quote, val))))
end

However, create_module(:MyMod) fails on Julia master (syntax error in eval), and crashes non-deterministically on 0.2 stable. Actually my test cases running inside Gtk.jl mostly never crashes, but the above code usually segfaults when run on its own in a fresh interactive 0.2 session. (under arch linux 64bit)

is there a better way to dynamically generate a module (and populate it with constants, etc)? Or maybe I should just wait for #1974 ?

[JeffBezanson]

I wouldn't generate the module by trying to poke at it externally with eval, but rather by using metaprogramming within the generated module. For example, see base/linalg/lapack.jl, which uses macros and @eval to generate wrappers.

Generating top-level expressions with eval is tricky. This works (although not recommended):

function create_module(modname::Symbol)
    eval(Expr(:toplevel, :(module ($modname) end), modname))
end

[bfredl]

Thanks! But eval( Expr(:toplevel, :(module MyMod; const myconst = var ...; end))) seems to sometimes put the constants in the parent module instead (on master). I'll try to isolate a test case later. (I understand why you recommend against it, #1974 will be better solution if it gets implemented)

[bfredl]

sorry, that was on 0.2 (mixing up my julia executables), on master it works all fine. Thanks!

[filmackay]

To create a module in the root namespace use eval(Main, ...). Didn't know about Main, there you go..

module A
    function create_module(modname::Symbol)
        Expr(:toplevel, :(module ($modname) end))
    end

    e = A.create_module(:B)
    println(e)
    eval(Main, e)
end

B

#$(Expr(:toplevel, :($(Expr(:module, true, :B, :(begin 
#        eval(x) = top(Core).eval(B,x)
#        eval(m,x) = top(Core).eval(m,x)
#    end)))), :B))
#
# B