Problems with xpcall

Guides UI and Macro
1

I’m having difficulty with xpcall and hoping for some help. The fundamental problem is that xpcall calls the errorHandler() but does not pass to it the error message. So, to that extent, I’ve very much simplified my code in order to more easier diagnose the problem. This is the function to be wrapped by xpcall. Note that it specifically raises an error:

local function testXpCall(param1, param2 )
    error("This is an error.")
    return true
end

Here’s how I’m wrapping testXpCall with xpcall().
l

local status, result = xpcall( function() return testXpCall( param1, param2 ) end, utils.errorHandler )

Finally, here’s a simplified errorHandler:

function utils:errorHandler(errorMessage)
print( errorMessage )
return errorMessage
end

Here are the results of running the simplified code:

Error caught: nil
Status: false
Result: nil

Any insights would be very much appreciated.

2

Missed that real problem. Change:
function utils:errorHandler(errorMessage)

to:
function utils.errorHandler(errorMessage)

3

Thanks for looking at this. However, I am confused about how the ‘:’ syntax sneaked into the code I posted. So, just be clear the code with the ‘.’ syntax is what was posted in my request above. I ran it again, just to be sure.

So, my question still remains. It seems as thought the system isn’t passing the error message to the handler.

Thanks, again

4

You posted everything but the first snippet in blockquotes rather than code blocks. Edit your post and wrap you code in ```

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5

The : is in the function declaration (right below “Finally, here’s a simplified errorHandler:”), not the xpcall statement.

From the lua manual

The colon syntax is used for defining methods, that is, functions that have an implicit extra parameter self. Thus, the statement

function t.a.b.c:f (params) body end

is syntactic sugar for

t.a.b.c.f = function (self, params) body end

In other words, using the : syntax here, the function “swallows” the first argument it references (in this cast the error message) as an implied “self” parameter (xpcall doesn’t understand that the function is a method of a table)

6

Some example code

local utils = {}
function utils.OnError(err)
    return "|Cffff00ffError:|r " .. err -- returned if there is an error
end

local function testXpCall(param1, param2)
    local causeError
    print(param1, param2)
    print(causeError.Now) -- raise an error causeError is nil not a table
    return true
end

local status, result = xpcall(testXpCall, utils.OnError, "A", "B")
if not status then
	print("Oops:",  result)
end
1 Like