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digitalmars.D.bugs - [Issue 7878] New: A problem with purity and general templated algorithms

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7878

           Summary: A problem with purity and general templated algorithms
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc



This is a spinoff of the closed Issue 7864 , see there for more info.

This is not a bug report and it's not even a real enhancement request, it's
just a note to not forget a small but what I think real problem in D+Phobos. At
the moment I don't have suggestions to how improve the situation. Ideas are
welcome.


This is wrong D2 code:


class C {
    string str;

    this(string str_) {
        this.str = str_;
    }

    override int opCmp(Object o) const {
        import std.string;
        auto rhs = cast(C)o;
        assert(rhs);
        return cmp(str, rhs.str);
    }
}

struct S {
    C c;

    int opCmp()(const auto ref S rhs) const pure {
        if (c < rhs.c) return -1;
        if (c > rhs.c) return 1;
        return 0;
    }
}

void main() {
    import std.algorithm;
    S[] stuff;
    sort(stuff);
}



DMD 2.059beta4 gives:

...\dmd2\src\phobos\std\algorithm.d(6802): Error: static assert  "Invalid
predicate passed to sort: a < b"
test.d(29):        instantiated from here: sort!("a <
b",cast(SwapStrategy)0,S[])


The error message looks correct, but it's really too much general, it doesn't
give enough information to the 
programmer, that is left to guess why the code doesn't work. This is quite bad.


To fix this program the first opCmp too must be pure:

    override int opCmp(Object o) const pure {

But in a little more complex program it risks being not easy to find such bugs.

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Apr 09 2012
next sibling parent d-bugmail puremagic.com writes:
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Kenji Hara <k.hara.pg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|DMD                         |Phobos



It is std.functional.binaryFun and std.algorithm.sort problem, not compiler's.

If the instantiation of predicate "a < b" that given to sort template function
is failed, they hide actual errors and instead print their own error messages
by static assert.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Jonathan M Davis <jmdavisProg gmx.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jmdavisProg gmx.com



PDT ---
That may be, but if overloaded operators are wrong (especially opEquals and
opCmp), I would expect the compiler to give errors for those types before any
instantiation of sort was even attempted, and clearly, that's not happening.

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Kenji Hara <k.hara.pg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull



https://github.com/D-Programming-Language/phobos/pull/544

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Apr 18 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Kenji Hara <k.hara.pg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrej.mitrovich gmail.com



*** Issue 5505 has been marked as a duplicate of this issue. ***

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Apr 20 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Commits pushed to master at https://github.com/D-Programming-Language/phobos

https://github.com/D-Programming-Language/phobos/commit/e2c892fdbfd23f45c2f304edb761b18111857228
fix Issue 7878 - A problem with purity and general templated algorithms

https://github.com/D-Programming-Language/phobos/commit/8e37bf3d01b59f620ed40bab8ee3943fab0289dc


Issue 7878 - A problem with purity and general templated algorithms

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Jun 04 2012
prev sibling parent d-bugmail puremagic.com writes:
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bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


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