Re: Q on functions as first class values

["Michael Newberry" <mnewberry@...>]

Actually, the instant after I sent that sage I realized that I cannot solve 
this issue by assigning a dummy value to the second call of SetTitle(), 
because that will just create another "alias" but not affect the first 
returned value. I could encapsulate the call in a metatable but that seems 
pretty elaborate to do what I want.

Michael Newberry

----- Original Message ----- 
From: "Michael Newberry" <mnewberry@axres.com>
To: "Lua list" <lua@bazar2.conectiva.com.br>
Sent: Wednesday, February 02, 2005 12:14 PM
Subject: Q on functions as first class values


> I think I have a found a limitation to the "functions as first class 
> values" design. Can someone please verify the following?
>
> Here is code that calls a C function SetTitle() three times. SetTitle() 
> sets a new string value in C-code and returns the previous one:
>
>    sOldTitle = SetTitle( "String 1" )
>    SetTitle( "String 2" )
>    SetTitle( sOldTitle )
>
> When SetTitle() is called the 3rd time to restore the title, it sets the 
> title to "String 2", not to sOldTitle, which is what I had intended.
>
> I think I see what is happening (is this correct?):  I have assigned 
> sOldTitle as the value of SetTitle(), so the fact that I did not update 
> sOldTitle by the second call to SetTitle() means that sOldTitle was 
> automatically updated by lua_pushstring() inside SetTitle(). Is this 
> correct? If so, then I could solve the problem by using a dummy value to 
> catch the unused return from the second call to SetTitle(). But I wonder 
> if there is a better way; otherwise that is a "gotcha" waiting to happen 
> again.
>
> Thanks,
> Michael Newberry