WoW:API pcall

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Calls a function, returning a boolean indicating success as the first return value, and error text / return values as the following values.

retOK, ret1, ret2, ... retn = pcall (func, arg1, arg2, ...);

Arguments

func: Function - The function that will be called (from within) pcall().
arg1 - argn: Variable - Any variable that is also to be passed with the function when its called (Optional).

Returns

retOK: Boolean - If the call to the function (that was passed to pcall) succeeded, returns true. If an error occured, returns false.
ret1: String (if failed) / Variable - If an error occured, error text is returned; if not, ret1 is the first return value of the original function.
ret2 - retn: Variable - If the function call succeeded, those return variables contain values returned by original function.

Example

function myTest(incrementVal)
  return incrementVal + 10;
end

local retOK, ret1 = pcall(myTest,"string value");
local msg = "";
if (retOK) then
 msg = "Function succeeded, result: " .. ret1 .. ".";
else
 msg = "Function failed, error text: " .. ret1 .. ".";
end
DEFAULT_CHAT_FRAME:AddMessage(msg);

Result

pcall will catch the error that occured within 'myTest', and output the appropriate text to the default chat window. If "string value" is replaced by a number, the code will output number+10 instead.

Details

pcall will also return other arguments returned from the "function" if all is successful.