The Case Against Autodecode

[Walter Bright via Digitalmars-d]

On 5/12/2016 9:29 AM, Andrei Alexandrescu wrote:
 > I am as unclear about the problems of autodecoding as I am about the necessity
 > to remove curl. Whenever I ask I hear some arguments that work well emotionally
 > but are scant on reason and engineering. Maybe it's time to rehash them? I just
 > did so about curl, no solid argument seemed to come together. I'd be curious of
 > a crisp list of grievances about autodecoding. -- Andrei

Here are some that are not matters of opinion.

1. Ranges of characters do not autodecode, but arrays of characters do. This is 
a glaring inconsistency.

2. Every time one wants an algorithm to work with both strings and ranges, you 
wind up special casing the strings to defeat the autodecoding, or to decode the 
ranges. Having to constantly special case it makes for more special cases when 
plugging together components. These issues often escape detection when 
unittesting because it is convenient to unittest only with arrays.

3. Wrapping an array in a struct with an alias this to an array turns off 
autodecoding, another special case.

4. Autodecoding is slow and has no place in high speed string processing.

5. Very few algorithms require decoding.

6. Autodecoding has two choices when encountering invalid code units - throw or 
produce an error dchar. Currently, it throws, meaning no algorithms using 
autodecode can be made nothrow.

7. Autodecode cannot be used with unicode path/filenames, because it is legal 
(at least on Linux) to have invalid UTF-8 as filenames. It turns out in the wild 
that pure Unicode is not universal - there's lots of dirty Unicode that should 
remain unmolested, and autocode does not play with that.

8. In my work with UTF-8 streams, dealing with autodecode has caused me 
considerably extra work every time. A convenient timesaver it ain't.

9. Autodecode cannot be turned off, i.e. it isn't practical to avoid importing 
std.array one way or another, and then autodecode is there.

10. Autodecoded arrays cannot be RandomAccessRanges, losing a key benefit of 
being arrays in the first place.

11. Indexing an array produces different results than autodecoding, another 
glaring special case.