On Thursday, 14 March 2013 at 17:07:16 UTC, Andrei Alexandrescu
wrote:
Very simple. Traditionally there's two crucial epochs known as
compilation time and run time. (There's some minor distinctions
like link time etc.) The whole notion of concepts and other
type systems for templates is predicated on three crucial
epochs: library compilation time, library user compilation
time, and run time. The logic goes, someone writes a generic
library and wants to distribute it to users. Users shouldn't
ever see bugs caused by e.g. typos in the library.
So the crowd that use meta-type systems is formed of library
writers who want to distribute libraries without ever
instantiating them. I don't think that's a good crowd to cater
for.
I've been surprised to figure how many people don't get this
flow, or only have a vague image of it. Although meta-types are
arguably "the right thing" to do, they're a lot less attractive
once it's clear what scenarios they help.
It is the very same reasoning. Meta-library developers are humans
and make mistakes. Forgetting to cover instantiating some corner
case in this example. If this won't compile, this bug won't
persist all the way down to the user of this library, exactly the
one we care most for.
