DIP 1009--Improve Contract Usability--Preliminary Review Round 1

[MysticZach via Digitalmars-d]

On Wednesday, 21 June 2017 at 04:16:22 UTC, Moritz Maxeiner wrote:
> What *I* need from a DIP that addresses DbC in D (to make it 
> viable for me) is to make the simple case as easy as possible 
> to read while not introducing language inconsistencies.
> With that in mind I am strongly in favor of the syntax H. S. 
> Teoh already proposed:
>
> ---
> int myFunc(Args...)(Args args)
>   if (Args.length > 2)
>   in (args[0] != 0)
>   in (args[1] > 1)
>   out (result => result > 0);
>
> int myFunc(Args...)(Args args)
>   if (Args.length > 2)
>   in (args[0] != 0)
>   in (args[1] > 1)
>   out (result => result > 0) { ... }
> ---
>
> - in contracts take a parenthesis delimited bool expression
> - out contracts take a parenthesis delimited bool function 
> literal.

`out` contracts would also have to account for the case where 
they don't check the return value. This would confuse the grammar 
a little in the case of function literals as boolean expressions. 
A different possible grammar that wouldn't have this problem is:

OutStatement:
     out ( IfCondition )
     out ( Identifier ) ( IfCondition )

plus the existing ones:

OutStatement:
     out BlockStatement
     out ( Identifier ) BlockStatement