why scope(success)?

[Daniel Keep]

I've been writing an OO binding to the cairo 2D drawing API, and
scope(success) has been a huge help.

Basically, cairo's api functions rarely if ever return an error code.
Instead, they set a flag on the object's pointer itself[1]_.  Since I
need to check this flag after every call I make on any particular
object, each wrapper class has a protected "checkStatus" member.  Then,
I just need to write this:

void someMember()
{
    scope(success) checkStatus();
    // ... do cairo stuff ...
}

When the "do cairo stuff" is just a simple function call, I don't really
gain anything.  But it comes in handy when I've got to return values
from cairo functions, or when I have to use any kind of complex logic.

Plus, I find reading "scope(success) checkStatus()" to be very clear;
that, and it's immediately obvious just looking at the code if I've
forgotten it (almost every function in the binding follows that pattern
so exceptions to that are easily spotted).

	-- Daniel

.. [1]: When I say "object" what I mean is that objects in cairo are
just pointers to undefined structs.  So a "cairo_pattern_t*" is an
"object" :P

P.S.  Cx looks very cool; must have a poke around that...

Ben Hinkle wrote:
> I hope this doesn't come of as a flame, but I'm wondering if anyone is using 
> scope(success) and why. I can't find any reason for it.
> 
> Some background: I've slowed my D work to focus on some C experimental 
> features I'm calling Cx: http://www.tinycx.org and currently I'm 
> implementing the error handling using reserved labels "error:" and 
> "finally:". The error label is roughly like scope(failure) and the finally 
> label is roughly like scope(exit). There's no try-catch-finally. I don't 
> plan on adding anything like scope(success) because I couldn't think of why 
> anyone would want to use it. Why not just put the code at the end of the 
> scope like normal code-flow? I suppose one could code the entire scope in 
> reverse just for kicks:
> void main() {
>   scope(success) printf("world\n");
>   scope(success) printf("hello ");
> }
> 
> -Ben 
> 
> 

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