Concat object is based on "luaL_Buffer". The luaL_Buffer documentation says:
During its normal operation, a string buffer uses a variable number of stack
slots. So, while using a buffer, you cannot assume that you know where the
top of the stack is. You can use the stack between successive calls to buffer
operations as long as that use is balanced; that is, when you call a buffer
operation, the stack is at the same level it was immediately after the
previous buffer operation. (The only exception to this rule is
luaL_addvalue.) After calling luaL_pushresult the stack is back to its level
when the buffer was initialized, plus the final string on its top.
So, the stack cannot be manipulated between the first call at the function
"luaL_buffinit()" and the last call to the function "luaL_pushresult()" because
we cannot known the stack status.
In other way, the memory used by these functions seems to be collected by GC, so
if the GC is triggered during the usage of the Concat object, it can be used
some released memory.
This patch rewrite the Concat class without the "luaL_Buffer" system. It uses
"userdata()" forr the memory allocation of the buffer strings.
49d4842e98