wierdness in debugger

[Rainer Schuetze via Digitalmars-d-ide]

On 30.03.2017 19:28, Enigma wrote:
> When debugging a foreach loop that works on an enum constant, the
> debugger has different behavior if the loop uses brackets or not
>
> The following should demonstrate it:
>
> import std.meta, std.algorithm, std.stdio;
> void main()
> {
>     enum X = AliasSeq!(1,2,3,4,5,3,2,1);
>     int y = 0;
>     foreach(x; X)
>        y = max(x, y);
>
>     writeln(y);
>
>     y = 0;
>     foreach(x; X)
>     {
>        y = max(x, y);
>     }
>
>
>     writeln(y);
> }
>
> a BP on the writeln lines will have the debugger skip to the writeln
> when stepping in the first case and not the second.
>
> It's as if the debugger thinks that the statement after the first max is
> part of the for each block or something weird like that. Was confusing
> at first and thought it was a bug because I was getting the wrong value
> for y. When, in fact, the BP on the writeln simply did not execute the
> foreach loop completely like it would in the second case, even though it
> should.
>

There is usually a jump instruction at the end of the for/foreach loop 
to return to the beginning of the loop. In the first loop this 
instruction does not have a respective token (with attached line info) 
that matches well in all cases:

- if you choose the "foreach" token, it can be very confusing as the 
jump instruction can also be the return address of the max() call and 
shown in the call stack.

- if you choose the next token "writeln" you get the confusion when 
executing the loop as you describe.

So it's a trade-off. Debugging C++ has the same issue and also sometimes 
seems to execute the statement after the loop.