Discrepancy between Defined()'s documentation and its behaviour with variables

[fvisagie]

The Defined() documentation (http://avisynth.nl/index.php/Internal_functions/Boolean_functions) indicates that it returns true or false for both function arguments and variables. When given the name of a defined variable it does return true, but an undeclared variable name causes the script to fail. Is this a bug or a documentation error?

false with function argument
function testfunc (int "testvar") {
return Defined(testvar) ? true : false
}
MessageClip(String(testfunc()))

true with defined variable
function testfunc () {
testvar = 0
return Defined(testvar) ? true : false
}
MessageClip(String(testfunc()))

Script error with undefined variable
function testfunc () {
#~ testvar = 0
return Defined(testvar) ? true : false
}
MessageClip(String(testfunc()))
I don't know what "testvar" means
(New File (2), line 3)
(New File (2), line 5)

[Gavino]

Script error with undefined variable
function testfunc () {
#~ testvar = 0
return Defined(testvar) ? true : false
}
MessageClip(String(testfunc()))
Here, testvar is not an 'undefined' variable (ie a variable with a value of 'undefined') - it simply does not exist.

Defined(), like all Avisynth functions, works on values, not variables.
As the documentation (http://avisynth.nl/index.php/Internal_functions/Boolean_functions) says, "the function returns false if its argument (normally a function argument or variable) has the void ('undefined') type, otherwise it returns true". See also the decription of the void or 'undefined' type here (http://avisynth.nl/index.php/Script_variables).

[fvisagie]

Thanks, Gavino. I'm reminded now of what stickboy does in his Undefined() function (which is built-in from 2.6.0).

[StainlessS]

RT_VarExist().
RT_Undefined() {useful on 2.58}
Also RT_FunctionExist() might be useful, plugins only (dont know how to do it for script functions although a dummy call might work).

EDIT: Eg,


myName="SC_SceneSelect: "
Assert(RT_FunctionExist("GScriptClip"),myName+"Essential GRunT plugin installed, http://forum.doom9.org/showthread.php?t=139337")


EDIT: So far as I'm aware, there is no way to tell if a variable is Global or Local from within a plugin, you can set either
Local or Global variables but only inquire if a variable exists, where Local is checked first and if fails then searches for a Global variable.
EDIT: Although using both PushContext and PopContext, you might be able to inquire directly the Global status.

[fvisagie]

This is what StickBoy did:
# JDL_FunctionDefined
#
# Determines whether a function is defined.
#
# PARAMETERS:
# functionName : The name of the function.
# Can be the name of a built-in function, a plug-in
# function, or a user-defined function.
# "err_msg" : If specified, JDL_FunctionDefined will throw an
# exception with that error message if the function is
# not defined.
# If not specified, JDL_FunctionDefined will return true
# if the function is defined, false otherwise.
#
# USAGE:
# # JDL_FunctionDefined can be used to check for script dependencies. If
# # a script requires a plug-in or function that isn't found, you can
# # present a meaningful error message explaining where to download the
# # necessary files.
# #
# JDL_FunctionDefined("Trim2",
# \ "This script requires Trim2. Download it from ...")
#
function JDL_FunctionDefined(string functionName, string "err_msg")
{
try
{
Eval(functionName + "()")

# If we made it this far, we called the function without any
# problem; therefore it exists.
return true
}
catch (s)
{
# Dependent on AviSynth generating an exception with the message:
# "Script error: there is no function named ..."
# Basic idea from mf.
isDefined = FindStr(s, "there is no function named "
\ + Quote() + functionName + Quote())
\ == 0

Assert(isDefined || !Defined(err_msg), err_msg)
return isDefined
}
}


The dummy call you referred to.

[StainlessS]

Yes, about the same as I was suggesting(but as a plugin).

[foxyshadis]

RT_VarExist().
RT_Undefined() {useful on 2.58}
Also RT_FunctionExist() might be useful, plugins only (dont know how to do it for script functions although a dummy call might work).

EDIT: Eg,


myName="SC_SceneSelect: "
Assert(RT_FunctionExist("GScriptClip"),myName+"Essential GRunT plugin installed, http://forum.doom9.org/showthread.php?t=139337")


EDIT: So far as I'm aware, there is no way to tell if a variable is Global or Local from within a plugin, you can set either
Local or Global variables but only inquire if a variable exists, where Local is checked first and if fails then searches for a Global variable.
EDIT: Although using both PushContext and PopContext, you might be able to inquire directly the Global status.

There's one direct way: Edit avisynth.h to add the first few private members of ScriptEnvironment to IScriptEnvironment as public (along with defining all of the new classes that brings in), then access var_table and global_var_table. It will only work for specific versions of Avisynth, and everyone will hate you, but it works!

The indirect is much more likely to actually keep working, though.

[StainlessS]

Dont temp me foxyshadis, I'm easily led astray.

and everyone will hate you
Not a problem, I'm used to it.

I might try the indirect route, thank you for your response.