[Issue 13185] Detect precondition violations at compile time when possible

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=13185

bearophile_hugs at eml.cc changed:

           What    |Removed                     |Added
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                 CC|                            |bearophile_hugs at eml.cc

--- Comment #1 from bearophile_hugs at eml.cc ---
(In reply to yebblies from comment #0)
> In many cases, the compiler can easily detect that a function call cannot
> possibly pass the precondition.
> 
> int divide(int x, int y)
> in
> {
>     assert(y != 0);
> }
> body
> {
>     return x / y;
> }
> 
> void main()
> {
>     func(3);
>     divide(9, 0);
> }
> 
> In these cases we can produce an error at compile time.

In my opinion it's much better to offer the programmer an explicit way to tell
the compiler that a compile-time testing (where/if possible) is desired, using
an "enum precondition":


int divide(in int x, in int y)
enum in { // Enum pre-condition.
    assert(y != 0);
in { // Regular pre-condition.
    assert(y != 0);
} body {
    return x / y;
}

void main() {
    divide(9, 0);
}

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