try/catch idiom in std.datetime

[Andrei Alexandrescu]

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.


Andrei