try/catch idiom in std.datetime

[Jonathan M Davis]

On Monday, November 18, 2013 14:45:54 Andrei Alexandrescu wrote:
> On 11/18/13 2:04 PM, Walter Bright wrote:
> > On 11/18/2013 1:02 PM, Jacob Carlborg wrote:
> >> I really don't understand the point in having some functions thrown
> >> and others
> >> assert.
> > 
> > That's a red flag that there is a faulty design somewhere, in this case
> > I think it's not having a separation between input data validation and
> > program bug detection.
> 
> The question is what's "program" and what's "input". Consider:
> 
> int a = fun();
> std.gun(a);
> 
> There are two possible takes on this:
> 
> 1. The standard library is considered part of the user's program, and
> the whole thing is a unit. In that case, passing the wrong int to
> std.gun is an PROGRAM error and 100% blame goes to the programmer who
> wrote the caller code. In that case, assert/assert(0)/contracts are the
> appropriate constructs to be used inside std.gun.
> 
> This is the approach taken by the C standard library, which is free to
> do whatever it wants (including crashing the program) upon calls such as
> strlen(NULL) etc.
> 
> 2. The standard library is a separate entity from the PROGRAM, and as
> far as it cares, any data from the user is INPUT. So the standard
> library with SCRUB the input, in which case enforce() and throwing
> exceptions are appropriate.
> 
> This is the approach taken by the Windows API, Java, C#, and to a good
> extent the newer parts of C++'s standard library.
> 
> To claim that one approach is exactly right and the other is exactly
> wrong would miss important insights.

+1

- Jonathan M Davis