Verbose checking of range category

[Gerrit Wichert]

Hello,

    maybe the template resolver can provide some kind of buffer where
the constrains can emit their messages to.
    If finally a match is found the buffer can be discarded. If not the
messages can be printed.
    So we only get messages for failed template instantiations.


Am 11.12.2010 18:15, schrieb Andrei Alexandrescu:
> Hello,
>
>
> Following Craig's questions about sort(), I was thinking of the
> following idea. How about defining a flag rangeCheckVerbose that emits
> explanatory messages during compilation whenever a range check fails?
>
> Consider this prototype:
>
> import std.stdio;
>
> version = rangeCheckVerbose;
>
> template isRandomAccessRange(T) {
>     enum isRandomAccessRange = isRandomAccessRangeImpl!T.value;
> }
>
> template isRandomAccessRangeImpl(T) {
>     enum hasEmpty = is(typeof(T.init.empty));
>     enum hasFront = is(typeof(T.init.front));
>     enum hasPopFront = is(typeof(T.init.popFront()));
>     enum hasIndexing = is(typeof(T.init[1]));
>     enum hasSlicing = is(typeof(T.init[1]));
>     enum value = hasEmpty && hasFront && hasPopFront && hasIndexing &&
> hasSlicing;
>     version (rangeCheckVerbose) {
>         static if (!value) {
>             pragma(msg, "Type " ~ T.stringof ~ " is not a random
> access range because:");
>             static if (!hasEmpty)
>                 pragma(msg, "  no empty property");
>             static if (!hasFront)
>                 pragma(msg, "  no front property");
>             static if (!hasPopFront)
>                 pragma(msg, "  no popFront method");
>             static if (!hasIndexing)
>                 pragma(msg, "  no indexing");
>             static if (!hasSlicing)
>                 pragma(msg, "  no slicing");
>         }
>     }
> }
>
> void main()
> {
>     writeln(isRandomAccessRange!int);
> }
>
> This program will generate a valid executable, but will also print
> during compilation:
>
> Type int is not a random access range because:
>   no empty property
>   no front property
>   no popFront method
>   no indexing
>   no slicing
>
> When a programmer has an odd issue with a range check, turning
> verboseness of checks could help.
>
> What do you think?
>
>
> Andrei
>