Minimized and explicit imports in std.algorithm

[andralex]

I'm investigating semi-automated ways to minimize dependencies, and worked on std.algorithm by hand. I was unable to figure what's needed from std.range. For the others, I either pushed them down into unittests or made the symbols explicit.

One simple advice for Effective D would be:

"Avoid using version(unittest) import xxx;. Instead, use import xxx; inside every unittest that needs it."

[dnadlinger]

I have a bad gut feeling about shipping this as long as http://d.puremagic.com/issues/show_bug.cgi?id=314 is still not RESOLVED FIXED.

[andralex]

@klickverbot good point. Could one of the compiler experts take a look at http://d.puremagic.com/issues/show_bug.cgi?id=314? @WalterBright? @9rnsr? @donc @AndrejMitrovic?

[monarchdodra]

Looking at the imports, I'd think a lot of these are probably only needed in specific functions. Using scoped imports would allow for safer (avoids bug 314), and more efficient (import only if used) imports.

In particular, I'm thinking about:

• import std.container : BinaryHeap; : Probably only used by very specific functions?
• import std.random : Random, uniform, unpredictableSeed; unittest only?

As for std.traits, we are using so much of it, I doubt a selective import is any useful.

[andralex]

For a vanilla non-unittest import of std.algorithm, dependencies now are down from 55 to 31. To compute these numbers I ran:

../dmd/src/dmd -I../druntime/import  -w -d -m64  -O -release -c -o- std/algorithm.d -v | grep '^import ' | cat -n

[andralex]

I can't further reduce dependencies because some symbols are used in restricted template guards, which cannot be scoped.

[ghost]

We should avoid imports in version(unittest) blocks at all costs. The tests will always run with -unittest, which means we'll never catch undefined symbols referenced by templates when not using -unittest (i.e. in user code). We've already had a few bugs like this pop up.

[monarchdodra]

We should avoid imports in version(unittest) blocks at all costs.

In this case 'AFAIK), the only place where it is used is followed by a debug(std_algorithm) import std.stdio;, so I think it should be fine. unittests are not run with debug=std_algorithm.

[monarchdodra]

That's a rather odd place to place a fully qualified import. This should go at the top I think. No one will go looking for an import in the middle of the file.

[andralex]

oops yes... shrapnel of various experiments.

[monarchdodra]

314 isn't fixed yet, is it? I like this, but I'm afraid that if we merge this right now, we'll leak symbols, leading to users writing code with incorrect imports...

For now, maybe we should leave the selective imports as global imports?

[monarchdodra]

There's a couple extra localized import std.traits you added in the code, which are useless with this import right here.

[andralex]

Presumably fixed Windows errors.

[andralex]

passes tests, ping pliz pliz

[9rnsr]

Unfortunately, this change silently breaks Phobos modules. Please see #1813 and merge it.